In brief: the Sayph phone takes a physical nano-SIM from any UK network (no eSIM). The SIM isn’t included, and it needs a plan with data: around 5GB a month should be sufficient for most children. This page covers choosing a plan, the networks we’ve tested ourselves, how to put the SIM in, and what to check if calls won’t connect.
On this page:
- What to look for in a plan
- Popular UK networks at a glance
- Networks we’ve tested with Sayph phones
- How to insert the SIM
- Calls not connecting? Check these first
We don’t sell SIMs – you buy your own and pop it in. That keeps you free to choose the network and plan that suit your family, and to change it whenever you like. The first half of this page is a friendly starting point for that choice: how much data to look for, what picture messaging and Wi-Fi Calling mean in practice, and how a few popular networks compare. The second half is for once the SIM has arrived.
Networks change their plans, prices and features often, so please treat this as a helpful starting point rather than a definitive or guaranteed source. Always confirm the latest details directly with the provider before you buy.
Sayph isn’t responsible for the accuracy of third-party information, and we don’t endorse or recommend any particular network – the networks below are listed to help you get started, not as recommendations. Do your own research to find the right fit.
What to look for in a plan
A Sayph phone is built for calls, texts, maps and radio – not for heavy browsing or streaming video – so you don’t need a big, expensive plan. Here’s a rough guide to the things worth thinking about.
| Consideration | What we’d suggest looking for |
|---|---|
| Data allowance | Around 5GB a month should be sufficient for most children. Maps and location use very little; lean towards more if they’ll stream a lot of radio or music. You almost certainly don’t need unlimited data. |
| Texts | Unlimited texts. This is standard on nearly every plan, so it’s rarely something you’ll need to pay extra for. |
| Minutes | Unlimited minutes, or a generous bundle. Calls to their approved contacts are one of the main things the phone is for. |
| Picture messages (MMS) | If your child will send or receive photos by text, look closely here. Most networks now charge for MMS or sell it as an add-on rather than including it; a few (such as Smarty and VOXI) include it. It’s easier to pick a plan that suits from the start than to add it later. |
| Wi-Fi Calling (VoWiFi) | Handy if home or school has weak mobile signal – it lets calls and texts work over a WiFi connection. See the note below the next table. |
| Contract type | A 30-day rolling SIM-only plan keeps you flexible and easy to change. We’d avoid long lock-in contracts for a first phone. |
| Cost | Low-cost SIM-only plans typically run about £2–8 a month, depending on the data and network. |
Popular UK networks at a glance
These are some of the networks and low-cost providers UK parents often consider. We’ve focused on two things that catch people out: whether picture messaging (MMS) is included, and whether Wi-Fi Calling is supported. Everything here can change, so do check before buying.
| Provider | Network used | Picture messages (MMS) | Wi-Fi Calling (VoWiFi) |
|---|---|---|---|
| Smarty | Three | Included – free on all voice plans | Yes – on supported handsets |
| giffgaff | O2 | Not included – around 30p each (needs credit) | Yes – on supported handsets |
| Tesco Mobile | O2 | Not included – around 55p each | Yes – pay monthly |
| VOXI | Vodafone | Included – unlimited on all plans | Yes – for eligible customers |
| iD Mobile | Three | Not included – charged per message* | Yes |
| EE | EE (own network) | Not included – around 83p each; a photo-message add-on is available | Yes |
| O2 | O2 (own network) | Not included as standard – charged per message, or add a 50-MMS bolt-on (around 10p each) | Yes |
| Three | Three (own network) | Not included – charged per message | Yes |
| Vodafone | Vodafone (own network) | Not included on most plans – around 75p each, or add an unlimited picture-message extra (not on Basics) | Yes |
Networks we’ve tested with Sayph phones
The comparison above is what the networks say about themselves. This table is what we have checked ourselves, by putting a SIM into both Sayph handsets – the Samsung Galaxy A16 4G and the Galaxy A17 5G – and trying the two features that most often catch people out. We only list what we have confirmed, and we’ll add networks as we test them.
| Network | Wi-Fi Calling | Picture messages (MMS) | Handsets | Confirmed |
|---|---|---|---|---|
| Smarty | Works | Works | Galaxy A16 4G and Galaxy A17 5G | September 2026 |
| VOXI | Not yet tested | Not yet tested | – | – |
Compare plans yourself
The best deals change all the time, so it’s worth comparing live prices on an independent site. These let you filter by data, price and network:
- MoneySavingExpert – Cheap SIM-only finder
- Uswitch – SIM-only deals
- MoneySupermarket – SIM-only deals
How to insert the SIM
You’ll need the nano-SIM and the small metal SIM tool from the phone’s box (a straightened paperclip does the same job). It takes about a minute.
- Switch the phone off if it is on.
- Find the SIM tray on the edge of the phone. It’s a thin slot with a tiny pinhole beside it.
- Push the SIM tool firmly into the pinhole until the tray pops out a little, then pull it out.
- Lay the nano-SIM in the SIM slot of the tray, gold contacts facing down, with the cut-off corner matching the shape of the slot. It only fits one way, so don’t force it. (The same tray has a slot for a microSD card, which is how you add music – see Sayph Music.)
- Slide the tray back in the same way round it came out, until it sits flush with the edge of the phone.
- Switch the phone on. Within a minute or so the network name and signal bars should appear at the top of the screen.
- Turn on mobile data: Settings → Connections → Data usage → Mobile data. Picture messages and location away from WiFi need it. Full detail in turn mobile data on.
Two things worth knowing. If your SIM arrived in a larger card, press out the nano-SIM (the smallest size) and use only that; micro and standard SIMs won’t fit and shouldn’t be trimmed. And a brand-new SIM sometimes needs activating with the network first, following the instructions that came with it. Activation can take a few hours, during which the phone may show ‘No service’.
Calls not connecting? Check these first
In brief: when a call won’t connect on a Sayph phone, the cause is nearly always the SIM or the network rather than the handset. The phone is standard Samsung hardware; Sayph decides who can be called, not whether the call gets through. These checks take five minutes and usually find it.
- Is the number an approved contact? The Sayph phone only calls and texts contacts you have approved in Sayph Space. In school mode it’s narrower still: only the contacts you’ve set as emergency contacts. If the number isn’t approved, the phone is doing exactly what it should. Approve the contact and try again.
- What does the top of the screen say? Look for the network name and signal bars. ‘No service’, ‘Emergency calls only’ or no bars at all means the phone isn’t registered on the network. Take the SIM out and reseat it (steps above), then restart the phone. Switching aeroplane mode on and off is a quicker way to make it reconnect.
- Is the SIM active and the plan paid? A new SIM may still be activating. A pay-as-you-go SIM needs credit, and a rolling plan needs the month’s payment to have gone through. The network’s own app or website shows the status of the SIM and plan.
- Is the signal weak where you are? If the phone shows one bar or fewer at home, switch on Wi-Fi Calling: Settings → Connections → Wi-Fi Calling. Calls and texts then go over your WiFi. It works only if the network supports it (see the tables above).
- Swap test. Put the SIM in any other phone. If calls fail there too, the problem is the SIM or the network. Or put a SIM you know works into the Sayph phone: if that one calls fine, again it’s the SIM or the network.
If the checks point at the network, contact them rather than us: they can see whether the SIM is registered and whether anything is wrong with the account. Tell them your number, that the handset is a Samsung Galaxy A16 4G or Galaxy A17 5G, what the screen shows, and what you’ve tried. If a SIM that works in another phone won’t work in the Sayph phone, that’s the one case that’s ours – email us with the same details.
A few practical tips
- The Sayph phone uses a physical nano-SIM only – there’s no eSIM support – and works on all major UK networks (EE, Three, O2, Vodafone and the providers that run on them).
- If you live somewhere with patchy mobile reception, check the plan supports Wi-Fi Calling before you commit, so calls and texts still work over WiFi.
- Calls and texts work on any SIM, but live location, maps and picture messages need mobile data switched on to work when your child is away from WiFi (picture messages need it even at home). You don’t need a big allowance – just a little data goes a long way. See turn mobile data on.
- If you think your child may want to send picture messages, choosing a plan that includes MMS from the start is simpler than adding it later.
Email help@sayph.one and tell us the handset (4G or 5G), the SIM network, what the top of the screen shows, and whether the SIM works in another phone. We’ll get you sorted.
Last updated: 13 September 2026.
New to Sayph? Work through your first ten minutes – the whole setup on one page. More answers on the Support Centre or the FAQ.
