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Mobile-phone contract checklist

UK mobile phone deals are usually listed by the monthly price and quota of data, voice minutes and SMS message fragments ("texts"), but you might want to check the small print for the following additional details:
Back-end provider
Relevant to MVNO deals (MVNOs can change their upstream providers but this is rare)---check the signal is good in areas you care about.
  • In Cambridge, Vodafone had the best signal last time I checked---this also supplied MVNOs Lebara and TalkMobile.
  • If there are two of you carrying a phone each, you might wish to subscribe to two completely different networks (e.g. Vodafone and Three), to make it more likely that at least one of the two will have good signal when you travel together in rural areas. This might become less of a concern once they manage to make more "network sharing" deals.
Wi-Fi calling available?
Some buildings are conductive enough to attenuate all mobile networks, but make Wi-Fi available---if you use such a building then you might want to check the "Wi-Fi calling" options if your device supports it (see my notes on Wi-Fi Calling on Android).
  • Three let me turn on Wi-Fi calling (on a supported device) without any prior setup
    • This extends to their MVNO "iD Mobile" (as of 2020) but we did experience some problems with timely SMS reception on iD when only WiFi was available
  • Vodafone let me turn on Wi-Fi calling, but only after I'd spoken with their helpline about it (and it covered voice calls only, not SMS messages, but the device automatically sent SMS via the mobile network and weak signal was sufficient),
  • but Vodafone's WiFi calling did not extend to their MVNOs like Lebara, who said in 2020 they do not support Wi-Fi calling
Conference calling available?
3-way calling might occasionally be needed if you know a language spoken by immigrant families who might ask you to be a last-resort interpreter (I say "last resort" because my policy is to pass the job to the professionals whenever possible, but occasionally it just has to be me), or if you need to help someone "dial in" to something when they themselves don't understand how to do it. But not all networks allow conference calling so it's worth checking before you sign up.
  • I was able to place conference calls on Three (and on iD) without any prior setup
  • Vodafone also allowed me to make conference calls, but required a call to the help desk to enable it. They later enabled conference-call activation via their website (under Dashboard / Controls and limits, check the conference-call limit is off); the setting has been known to be reset from their side and need switching again. I've also experienced the phone saying "Unable to make conference calls" on one day but being fine again a few days later.
    • I've also experienced an instance of one specific private landline number not being allowed to be added to any conference call, although conference calls were otherwise working (and the landline number in question could be added to conference calls placed from an H3G number).
  • Lebara in 2020 said I can activate conference calls by texting CONF to 38885---this replied "unexpected system error" the first two days I tried, but it worked on the third day.
  • MVNOs reselling EE's network did not provide conference calling last time I checked.
  • Multiple providers (at least Three and Vodafone) do not allow the use of DTMF tones while a conference call is in progress (tested with three different handsets from two manufacturers), so if one of the lines requires DTMF (for example if you are trying to help someone join a Zoom meeting by calling both them and Zoom) then you should take care of the DTMF button presses before adding the second line to the call.
Can you deactivate voicemail?
If any of your contacts are refugees, international students or others likely to have pay-per-minute phones, or older people calling from a landline without a calls package to mobiles, then you likely won't want them to pay for calls you didn't manage to answer, nor to take an immediate financial hit when you had no signal. Phone networks are motivated to make voicemail hard to opt out of (which might also be why many of the non-voicemail based services to log incoming calls when you had no signal, such as "Call Catcher" and 1471 for mobile, have now been shut down)---voicemail increases their "call termination" income (by counting as a "connected" call), and they think most callers won't mind because they're on unlimited-minutes or hundreds-of-minutes contracts. Ease of deactivating voicemail is (I think) an important facet of a mobile deal that's seldom advertised.
  • Vodafone voicemail used to be deactivated using standard GSM commands (often provided as Settings by phones), which could be reapplied if they switched it back on by mistake. In 2022 they changed their system so these codes are ignored and you'll need to call 1210 to turn off voicemail.
  • A Lebara SIM in 2020 actually came without voicemail being activated, which makes a nice change
  • When I deactivated voicemail on Three, their network ignored the GSM commands: I had to call the helpline and hold for nearly an hour, then speak with an operator who tried to persuade me to leave it switched on.
  • Disabling voicemail on iD Mobile was done via their website in 2020, and resulted in a call immediately disconnecting if the phone is off (no "this mobile is switched off" message or anything like that), sometimes displaying the message "number not valid." This is particularly unhelpful on the iPhone, which automatically rejects incoming calls when on silent (rather than letting them ring without sounding the ringer like normal phones do)---Apple does not provide any option to change that behaviour.
Extra charge for SMS delivery confirmation?
SMS delivery is not guaranteed, and if you're messaging someone who might have forgotten to tell you they've left the country (e.g. international students), or whose safety you're concerned about, then it can be useful to know if your message was delivered to a phone (meaning at least the service is still connected and the phone still has power---although I have seen some cases of networks sending misleading delivery acknowledgements for cancelled numbers). Some networks charge extra for requesting delivery confirmation---which can accumulate if you sent a lot of texts with that bit still switched on.
  • I have never known Vodafone to charge for delivery confirmation. Lebara also didn't do so in 2020.
  • Three started charging for delivery confirmation in 2011.
  • Orange did charge---Orange is now part of EE, but I haven't heard of EE as a whole charging for it (but check).
Can long SMS messages be sent?
Occasionally it is necessary to send someone a lot of text by SMS, e.g. if they have no data service and you need to send them a copy of an article. Although some devices insist on switching to the more expensive (and less widely-received) MMS protocol for this, with correct configuration you might be able to send a whole article by SMS---but only if the network supports it.
  • With Vodafone I've successfully sent SMS messages up to 127 fragments and without running into any per-day limits as a result.
  • Lebara's per-message limit (as of 2020) is somewhere between 95 and 99 fragments, and they have a hard limit of 200 fragments a day.
  • Last time I used LycaMobile, each sent SMS was limited to just 2 fragments.
What happens if "unlimited" fair-use limits are reached?
"Unlimited" is often just an advertising code for "we don't think normal people will reach the limit", which is typically listed in the small print as a "fair-use limit". Occasionally (e.g. if you suddenly have a lot of organising to do) you might get closer to it than you planned, so you might want to check what happens if you did reach it: will they just cut you off or will they bill you extra?
  • Last time I checked, Vodafone's "unlimited" meant 3000 minutes a month, beyond which they can bill but they warn you first.
  • Lebara's "unlimited" meant 3000 minutes and 1000 SMS-fragments a month, beyond which they'll bill without warning.
  • H3G (and MVNOs like iD) also cap each outgoing call to 2 hours, after which the call is stopped and must be placed again (which isn't normally a problem)
"Tethering" included?
Some data deals stipulate that the data must be used from the phone itself and not via a personal Wi-Fi hotspot or USB "tethering"---and yes they do have ways to enforce or punish this, so if you'll ever need to do it, you'd better check the contract supports it.
  • As of 2020 it seems allowing tethering is becoming more popular---the only MVNO I could find that still completely prohibited it was LycaMobile. Some other MVNOs limited it to less than your full data allowance on their larger plans, while the four core networks said you can use your full allowance.
195 access
If you have a disability that prevents you from using standard printed editions of "The Phone Book" then you should be registered for the 195 service (free directory enquiries)---and it's an Ofcom requirement that all networks (including MVNOs) carry these calls. Three and Vodafone let you pre-register your PIN with them so you don't have to give it each time (Vodafone used to start charging for the 195 call after 75 seconds but Ofcom required that to stop; still pre-registration saves operator time). I don't know of any MVNOs that support pre-registration, but you can still call 195 and provide your PIN in the normal way.
The above is based on my experience---E&OE.
All material © Silas S. Brown unless otherwise stated.