SMS API Service: The Ultimate Checklist
Who knew there’d be 7 whole points to make about SMS API services? In fact, most providers look identical on paper – you send a text, you get a delivery report and the job is done.
But it isn’t as black and white in the SMS world because you need to notice the small print. That includes the rules around the texts you pay, credits that quietly expire, and an apostrophe that doubles the cost of a message (see point 5, the Unicode trap). You usually only find these things after you’ve integrated, tested and gone live.
So here’s a checklist for judging any SMS API service before you write a line of code. We’re an SMS API provider, but every point below is a question you can put to any supplier, us included. If you want the bigger picture first, our complete guide to SMS APIs covers how they work.
1. You only pay for texts that are delivered
This is the big one. Across the industry, almost 10% of texts don’t get delivered. This is pretty standard because things like numbers getting ported, phones being switched off for good, or people typing their mobile number wrong on a form.
Most providers still charge you for those messages, even though the networks don’t charge them. On a send of 100,000 texts, that can mean paying for 10,000 messages nobody read. The reasons for this may vary, but this is where we have a different approach.
2. Delivery reports you can act on
A good SMS API service tells you more than just if a message was sent. You should see the final delivery status of every message, why it failed and what it cost. That turns your delivery reports into a data-cleaning tool, where you can spot dead numbers, fix them and stop paying to text them (if you choose a different SMS API provider to us, of course).
3. Credits that don’t expire
Some providers sell credits that vanish after 12 months. If your volumes are seasonal or unpredictable, you end up either overbuying and losing the balance or underbuying and topping up at worse rates. It’s like hoarding your Christmas decorations in the attic, only to find that come November, they’re about to disappear. That’s not very helpful.
The meaning of ‘expiry’ can vary from one provider to another, as some will just need an active account (e.g. sent a message, even a test, over the last 12 months), whereas others may just give you a deadline. Not entirely sure of what each SMS API provider offers, as this changes all the time, but it’s worth looking at the terms and conditions for that one.
4. No hoops for sender IDs
Your sender ID is the name your message appears to come from, like ‘YourBrand’ instead of a random number. Some services make you register every sender ID in advance and wait for approval. That’s not necessarily noticeable until marketing wants a new one on a Friday afternoon for a client.
For UK delivery, you don’t always need to register sender IDs at all.
5. Protection from the Unicode trap
A standard text holds 160 characters. Use a single non-GSM character, such as a curly apostrophe pasted from Word, and the whole message switches to Unicode. Your limit drops to 70 characters and a 150-character message suddenly costs three credits instead of one.
It happens constantly, because content teams write in tools that ‘smarten’ punctuation automatically. Or maybe using a generative AI tool that pulls a pesky Unicode character through.
6. UK routes and UK data
Grey routes are cheap, indirect paths that bounce your texts through other countries. They’re behind a lot of ‘’too good to be true’ pricing, and they often have a negative impact on delivery rates and speed.
If your customers are in the UK, look for direct, tier-one connections to UK networks and UK-based servers. It’s better for delivery and it makes your GDPR conversations far simpler.
7. An API you can integrate in an afternoon
A good SMS API service is boring to integrate, but in the best way. The type where you can roam through the docs with a cuppa in hand. Clear documentation, a simple REST endpoint, SDKs for your language and a free trial so you can test with real phones.
Red flags when comparing SMS API services
Cheaper than the rest
‘Unlimited’ or suspiciously cheap bundles compared to the majority of providers. Rock-bottom prices often rely on grey routes, so make sure you ask where your texts actually go.
Unnecessary subscriptions
Not just any subscription, but one that others offer as standard. Minimum contracts or monthly fees for an API. Pay-as-you-go should be the norm for most businesses.
Invisible resources
No public documentation. If you can’t read the API docs before signing up, expect the integration to be harder than promised.
Support that’s sales in disguise
When something breaks at 9pm, you want an engineer, not an account manager.
Not sure you need an API at all? If you’re sending occasional campaigns by hand, you might be better off with web SMS instead of an API.
SMS API service FAQs
What is an SMS API service?
An SMS API service lets your software send and receive text messages automatically. Your app makes a simple web request, and the provider delivers the text to the mobile network. It’s how businesses send things like login codes, appointment reminders and delivery updates.
How much does an SMS API service cost in the UK?
UK providers typically charge a few pence per standard 160-character text, with lower rates at higher volumes. The number that matters is cost per delivered message, so factor in whether failed texts are refunded. Our SMS Price Calculator shows what your volumes would cost.
What’s the difference between an SMS API and an SMS gateway?
In practice, nothing. The terms are used interchangeably for a service that connects your software to the mobile networks.
Can an SMS API service receive replies?
Yes, if the provider offers virtual mobile numbers or shortcode keywords. Replies can be forwarded to your system by webhook or email.
Can I send texts outside the UK?
Usually, but international texts typically cost more than one credit and some countries have their own rules. See our guide to sending to non-UK numbers.
Try an SMS API service that passes its own checklist
We built The SMS Works because we were fed up of paying for texts that never arrived. Undelivered UK messages are refunded automatically, credits don’t expire, sender IDs need no pre-registration, and everything runs on UK servers with direct network connections.
Sign up free and you’ll get 50 test credits, enough to run every check on this page. Most developers send their first message within minutes.