If you’ve requested it then you may start seeing network names like this showing up on your phone. From what we can see it seems that you get “Orange T-Mobile” when you cross over from Orange to T-Mobile and “T-Mobile Orange” when you’re a T-Mobile customer doing the reverse.
As Dan mentioned yesterday this hasn’t kicked in for those of you who signed up earlier. You need to sign up at orange.co.uk/share or tmobile.co.uk/share depending on who you are with to activate your SIM. Once done, it’ll roam across to the other network when you lose signal on your primary network.
Update – Loads of questions on this. Currently this is 2G roaming only. Both networks state, “You might get some basic, slow internet and data services” when roaming. Basically put, you get texting, voice and GPRS probably – no 3G yet, but they are pushing hard on this and will be pushing all customers across to the new merged network soon, whether you’ve opted in or not. There are some small side-effects, but they come from some handsets believing that they are roaming internationally even though you are still in UK..
Link – Larger pics