How to migrate from GMS to Sinch

GMS is a Switzerland-based enterprise CPaaS and A2P messaging provider that exposes SMS, RCS, WhatsApp, Viber and email through a single REST API. Sinch is a cloud communications platform offering messaging, voice and email APIs across a wider channel and regional footprint. On the messaging.dev Score, GMS rates 36/100 and Sinch 92/100; the sections below lay out what actually differs so you can plan the move.

What you gain and what you lose

Channels first, because that is the biggest structural change. Both providers cover SMS, RCS, WhatsApp, Viber and email, so you lose no channels by moving. You gain MMS, Facebook Messenger, Telegram, Apple Messages for Business and voice — five channels GMS does not offer.

Compliance is a superset: both hold GDPR and ISO 27001, and Sinch adds SOC 2 and HIPAA. No certification is lost in the move.

Data residency widens. GMS runs EU servers only, with no region choice. Sinch offers both EU and US servers, explicit data-residency choice, and additional regions (APAC, Australia, Brazil).

Commercially, the model changes shape. GMS uses custom enterprise pricing negotiated with sales, with no public price list and no self-onboarding. Sinch is self-service pay-as-you-go per message (with volume and committed-use tiers), publishes a starting rate of roughly $0.0075 per US SMS segment plus carrier fees, and includes free developer credit — GMS offers none.

Tooling differs too. GMS ships mobile SDKs (iOS/Swift, Android/Kotlin) and REST only; Sinch ships server-side SDKs (Java, Python, C#, Node.js, PHP), adds SMTP and SMPP alongside REST, provides a sandbox (GMS has none), and its docs are rated high versus GMS’s medium. See how to start with Sinch for the full onboarding path.

How the request format differs

GMS quickstart:

curl -X POST 'https://api-v2.hyber.im/{client_id}' \
  -u 'CLIENT_ID:API_PASSWORD' \
  -H 'Content-Type: application/json' \
  -d '{
    "phone": "380631010100",
    "channels": ["sms"],
    "sms": {
      "sender": "MyBrand",
      "text": "Hello from GMS",
      "ttl": 300
    }
  }'

Sinch quickstart:

curl -X POST 'https://us.sms.api.sinch.com/xms/v1/YOUR_SERVICE_PLAN_ID/batches' \
  -H 'Authorization: Bearer YOUR_API_TOKEN' \
  -H 'Content-Type: application/json' \
  -d '{"from":"+15005550006","to":["+15551234567"],"body":"Hello from Sinch"}'

Three things change:

• Endpoint. GMS posts to https://api-v2.hyber.im/{client_id}, keyed by client ID. Sinch posts to https://us.sms.api.sinch.com/xms/v1/{service_plan_id}/batches, keyed by a service-plan ID in the path.
• Authentication. GMS uses HTTP Basic auth (Authorization: Basic base64(client_id:password), passed as -u CLIENT_ID:API_PASSWORD). Sinch uses a Bearer token (Authorization: Bearer YOUR_API_TOKEN).
• Payload mapping. GMS nests everything under a channel object: the recipient is phone (bare digits), and sender/text live inside an sms block selected by a channels array. Sinch flattens this: the sender becomes top-level from, the recipient becomes to as an array of E.164 numbers (with a leading +), and the message becomes top-level body. GMS’s ttl field has no equivalent in the minimal Sinch batch call.

Migration checklist

1. Create a Sinch account (self-onboarding) and generate an API token and service-plan ID; note the free developer credit for testing.
2. Choose your region — the documented endpoint is US-hosted, so pick the EU region if you need EU residency.
3. Map the request fields: phone → to[], sms.sender → from, sms.text → body; drop the channels wrapper and ttl.
4. Swap Basic auth for the Bearer token and re-point the base URL in your sending code.
5. Re-test against the Sinch sandbox before sending live traffic.
6. Update delivery/status webhooks to Sinch’s callback format.
7. Run GMS and Sinch in parallel, compare delivery, then cut over.

Watch out for

• Default US endpoint. The quickstart base URL is us.sms.api.sinch.com. GMS was EU-only; if residency matters, explicitly select Sinch’s EU region — the choice exists, but the documented default is US.
• No native mobile SDK. GMS’s Swift and Kotlin SDKs have no direct Sinch equivalent; the listed SDKs are all server-side (Java, Python, C#, Node.js, PHP), so mobile apps call the REST API directly.
• Metered billing. You move from a negotiated enterprise contract to pay-as-you-go (~$0.0075 per US SMS segment plus carrier fees); model your volume before cutover.
• Published SLA. Sinch publishes a 99.95% uptime SLA; GMS claimed 99.99% but published no formal SLA — compare both against your requirements.

Full side-by-side: GMS vs Sinch.