In reply to FreshSlate:
I don't want to jinx it by saying
'it's *ixed", but I got it back this evening and it's working...so far. Ssssh!
The problem was for the past 3 and a half months, the mobile data connection has been switching itself off at random. Initially it was only every so often, but for the last 3 weeks, it was continuously, and whenever you tried to make a call or surf. Virgin finally relented and took it in for repair 2 weeks ago. I got it back a week later and despite them saying it had been fixed, as soon as I switched it back on it displayed the same old problems and had no connection. Swapping the SIM into an old HTC handset sorted the issues, so it wasn't the SIM card or the reception. I'd told them this several times on the phone to the "help-desk" <insert choice words here>, and finally they took it back again at the beginning of this week. Got it back a couple of hours ago and so far, so good.
There were a few other problems too, in that it sometimes thought 'flight mode' was activated when it wasn't, but I still couldn't make a call. When I tried to activate 'mobile data connection' it told me to insert SIM card, even though one was already in. The weirdest one was an error message that would appear at random saying: "RESET_BY_IPC_TIMEOUT. Please get ril log/data/log/dumpstate_Reset by IPC timeout_date.log"
The 2nd line response tech guy on the help-desk had to resort to googling this and found some site in Spanish referring to it. He proceeded to ask me if I could translate!
Not sure what they've done or found this time, but fingers crossed it's going to last. As I said before, when it's working it's a great phone.