When you’re building your first app, Firebase SMS OTP feels like the easiest way to add phone number verification: simple APIs, generous free credits, and seamless integration with Google’s ecosystem. It’s no surprise that many startups choose it to secure logins or sign-ups without worrying about telecom providers.

But as your user base grows, cracks start to appear. SMS costs can snowball once you move beyond the free tier, routing is limited in some regions, and flexibility often takes a backseat to convenience. What worked for a small MVP can quickly turn into a bottleneck at scale.

The good news: you’re not stuck. In 2025, a strong ecosystem of SMS OTP providers exists, each designed with scalability, transparency, and global reliability in mind. In this guide, we’ll explore the 10 best alternatives to Firebase SMS OTP, so you can keep your users secure while controlling costs and ensuring delivery worldwide.

What is Firebase SMS OTP?

Firebase SMS OTP (One-Time Password) is Google’s service for sending temporary verification codes by SMS to confirm a user’s identity. Think of it as a digital key delivered straight to your phone: unique, short-lived, and secure. 

It’s important to note that SMS OTP is not Firebase’s core feature. Firebase is primarily a Backend-as-a-Service (BaaS) offering hosting, databases, and developer tools, but OTP is one of the most popular authentication options used by mobile apps.

For developers, Firebase SMS OTP is appealing because it abstracts away the complexity of dealing with telecom providers, retries, or regional delivery issues, so you can focus on building features instead of managing SMS gateways.

In a typical authentication flow:

• A user enters their phone number in your app,

• Firebase sends a one-time code via SMS,

• The user inputs the code to verify their identity and complete login.

The appeal is clear: easy integration, Google Cloud reliability, and a free tier that’s perfect for small apps or MVPs. These strengths explain why Firebase SMS OTP has become a go-to solution for many early-stage teams.

The problem with scaling on Firebase

At first, Firebase SMS OTP feels like the perfect fit: quick to set up, free to start, and backed by Google’s infrastructure. But as your app gains traction, the experience changes. What seemed effortless at launch can become a costly and rigid setup when you need to scale.

Problem: when costs start to spiral

Beyond the free tier, SMS authentication costs rise steeply, and performance may lag for apps with global users. What felt like a shortcut early on can turn into a long-term bottleneck.

Agitate: the hidden frustrations of growth

For growing teams, the challenges pile up fast:

• Exponential pricing for SMS OTPs makes every new user feel expensive,

• Limited flexibility in routing messages can hurt delivery in some regions,

• Little control over data location, creating compliance and latency concerns.

It’s like moving into a starter apartment that once felt spacious, until you realize the walls don’t stretch as your family grows.

Solution: a better way forward

The answer isn’t to abandon OTP altogether, but to look at specialized providers that scale better. These platforms bring transparent pricing, flexible multi-routing, and stronger compliance controls, while keeping the ease of OTP authentication that developers rely on.

How to choose the right Firebase SMS OTP alternative?

Not every OTP provider is built the same. Once you move beyond Firebase’s built-in OTP service, the real challenge is knowing which platform fits your product’s needs at scale. The best choice balances cost, delivery performance, and security, while giving your team more control than Firebase’s default setup.

Here are the key factors to evaluate:

• Pricing transparency and scalability: look for providers with clear per-message pricing and volume discounts. Surprise bills are the last thing a scaling startup needs,

• Delivery and routing performance: OTPs are useless if they don’t arrive. Multi-routing and carrier partnerships make a big difference in global reliability,

• Fraud prevention: features like SMS pumping protection or disposable number detection protect both your budget and your users,

• Data compliance and security: ensure the provider supports standards like GDPR or SOC 2, and offers data residency options if needed,

• Developer experience: clean APIs, SDKs, and good docs save weeks of engineering headaches,

• Support and SLAs: if OTP is critical to your product, look for responsive support and clear uptime guarantees.

By weighing these factors, you can identify an alternative that not only replaces Firebase SMS OTP, but also gives you the freedom to scale with confidence.

Top 10 Firebase SMS OTP alternatives compared

When teams outgrow Firebase’s built-in SMS service, they often turn to specialized OTP providers. While Firebase is excellent for core app infrastructure, SMS OTP is only a side feature, not its main focus. As your verification traffic grows, costs, routing limits, and compliance hurdles start to show.

That’s where dedicated providers come in: platforms built for reliable OTP delivery, global scale, fraud prevention, and transparent pricing. They’re the natural next step once your authentication needs move beyond Firebase.

Here are the top 10 providers to consider in 2025:

1. Prelude

Prelude is built specifically for scalable, secure OTP delivery. Unlike Firebase, which treats SMS OTP as a side feature, Prelude makes authentication its core business, offering multi-routing for better delivery, real-time anti-fraud checks, and SOC 2 compliance. Its developer-first APIs make it easy to integrate while keeping costs predictable.

• Strengths: affordable pricing, advanced fraud detection, multi-channel OTP (SMS, email), SOC 2 compliance,

• Ideal for: startups and SaaS scaling rapidly without wanting costs to spiral,

• Pricing: Prelude starts at €0.03 per verification (pay-as-you-go), with volume discounts in the Startup plan (€100/month+). Enterprise plans offer custom rates and SLA-backed support.

2. Twilio

One of the most well-known CPaaS providers, Twilio powers billions of messages worldwide. Its Verify API simplifies OTP flows with support for SMS, voice, and email, plus add-ons like fraud prevention and adaptive routing.

• Strengths: global reach, multi-channel verification, strong developer ecosystem,

• Ideal for: enterprises and apps needing flexible, programmable communications,

• Pricing: Twilio uses pay-as-you-go pricing starting at $0.0083 per SMS in the US, with volume discounts down to $0.0073 per message. Additional carrier fees may apply.

3. Vonage

Previously Nexmo, Vonage offers SMS and voice verification APIs with two-factor authentication (2FA) support. It’s widely adopted for international OTP delivery and integrates easily into mobile and web apps.

• Strengths: reliable global delivery, flexible OTP channels, enterprise-ready,

• Ideal for: apps with global user bases that need consistent verification,

• Pricing: Vonage uses pay-as-you-go pricing that varies by destination, for example, about $0.081 per SMS to France. Enterprise add-ons like Audit API or Redact API are available separately.

4. Infobip

Infobip is a global cloud communications platform trusted by banks, fintechs, and large enterprises. Its Verify API includes SMS OTP, voice, WhatsApp, and email, plus advanced routing and compliance features.

• Strengths: multi-channel OTP, enterprise-grade compliance, global presence,

• Ideal for: fintechs, e-commerce, and regulated industries,

• Pricing: Infobip follows a pay-as-you-go SMS model with rates that vary by country. It also offers add-on modules like Moments (from €49/month), Conversations (from €39/month), and Answers (from €99/month).

5. MessageBird

MessageBird provides an omnichannel platform with a strong focus on SMS and verification APIs. It allows OTP delivery across SMS, WhatsApp, and email, with analytics and delivery optimizations.

• Strengths: omnichannel verification, strong European presence, good analytics,

• Ideal for: businesses targeting European and global markets,

• Pricing: MessageBird offers pay-as-you-go SMS (€0.0317 per message in France) and WhatsApp (€0.1558 per message). A Marketing plan starts at €45/month for 3,000 contacts, with custom pricing available for enterprises.

6. Sinch

Sinch specializes in mobile engagement and verification, handling billions of messages annually. Its OTP API includes SMS, flash calls, and data verification, making it highly flexible for global apps.

• Strengths: scalable OTP, flash call verification, fraud prevention tools,

• Ideal for: apps looking for alternatives beyond SMS-only OTP,

• Pricing: Sinch charges pay-as-you-go, e.g. $0.065 per outbound SMS and $0.032 per inbound SMS in Singapore. Numbers cost a $10 setup fee plus $50/month, with custom pricing available for high volumes.

7. Telesign

Telesign focuses on identity and communication APIs, offering SMS OTP with strong fraud detection (phone reputation scoring, number intelligence). It’s particularly strong for security-first industries.

• Strengths: security-focused, fraud scoring, strong compliance framework,

• Ideal for: companies prioritizing fraud prevention with OTP,

• Pricing: Telesign SMS starts at $0.0072 per message on a pay-as-you-go model, with volume discounts and custom enterprise plans available.

8. Kaleyra

Kaleyra is a global CPaaS provider delivering SMS OTP, voice, and push verification. With clients in finance, healthcare, and retail, it offers enterprise-level compliance and routing optimization.

• Strengths: reliable OTP delivery, compliance with financial regulations, global reach,

• Ideal for: large enterprises with compliance-heavy needs,

9. Plivo

Plivo provides SMS APIs with a focus on cost efficiency and global delivery. Its Auth API supports SMS and voice OTP verification, with transparent pricing and developer-friendly documentation.

• Strengths: cost-effective, easy to integrate, strong API support,

• Ideal for: startups and SMBs looking for affordable OTP delivery,

• Pricing: Plivo SMS starts at about $0.0066 per message in the US (inbound SMS free). Monthly plans range from $25/month (Starter with $10 credits) to $999/month (Enterprise with OTP APIs, custom sender IDs, and discounts).

10. Mitto

Mitto is a global SMS and messaging provider with a strong focus on reliable OTP delivery. It combines direct operator connections with intelligent routing to maximize delivery rates worldwide. Known for its transparent pricing and enterprise support, Mitto is often chosen by brands that need cost-efficient verification at scale.

• Strengths: strong global coverage, reliable OTP delivery, competitive pricing, operator partnerships,

• Ideal for: businesses needing affordable and reliable SMS OTP with enterprise-grade support,

• Pricing: Mitto uses a pay-as-you-go model with destination-based SMS rates in USD. Pricing scales with usage, and volume discounts or custom enterprise quotes are available for high-traffic customers.

Comparing Firebase SMS OTP alternatives

While Firebase offers SMS OTP as a secondary feature, specialized providers deliver stronger performance, flexibility, and pricing transparency. Below is a comparison of 10 leading SMS/OTP-focused providers.

FAQs about Firebase alternatives

Is Firebase SMS OTP free forever?

No. Firebase includes a free tier with limited OTP sends, but once your app grows beyond that, costs can rise quickly. Many teams are surprised by how expensive SMS OTP gets at scale.

What is the best alternative to Firebase SMS OTP?

It depends on your needs. If cost efficiency and global delivery are priorities, Prelude is a strong choice thanks to its multi-routing, fraud prevention features and OTP best practices. Other providers like Twilio, MessageBird, or Vonage are also widely used, but pricing and performance can vary.

Can I migrate from Firebase SMS OTP easily?

Yes. Most OTP providers offer straightforward APIs and SDKs, so swapping Firebase for another service is usually just a matter of adjusting integration logic. The main task is ensuring a smooth transition for existing users.

Does Firebase SMS OTP have limits?

Yes. Firebase sets quotas on OTP usage, and once you exceed them, you may face rate limits and higher costs. This is one of the main reasons fast-growing apps look for dedicated OTP providers.

Is Prelude a replacement for Firebase SMS OTP?

Yes, and often a better one at scale. Prelude is designed for transparent pricing, global delivery, and compliance, making it a reliable upgrade once Firebase’s OTP service becomes limiting.

Which Firebase SMS OTP alternative is best for startups?

For early-stage teams, providers with pay-as-you-go pricing (like Prelude) are usually the most startup-friendly. You only pay for what you use, without being locked into heavy monthly commitments.

Conclusion

Firebase is an excellent starting point: it lowers the barrier to entry with free credits, smooth onboarding, and solid developer tools. But as your app scales, the challenges become harder to ignore: rising costs, limited flexibility, and less control over your infrastructure.

The good news is that today’s ecosystem is rich with SMS/OTP-focused providers designed for growth. Prelude leads the way with secure, affordable, and globally reliable OTP delivery, while other providers like Twilio or MessageBird also offer robust global infrastructures. You now have more choice than ever to match your business needs.

In the end, the best option is the one that balances scalability, budget, and control for your specific use case. Choose the SMS/OTP solution that fits your scaling, budget, and security needs, so your product can grow without compromise.