Recently purchased an iPhone 3GS from another member here, and it's been working fine for the best part of the last month or so. It has officially been unlocked by O2.
However, as of some time this week, i've been unable to get anything more than a flat five-bar signal - meaning no calls/texts in or out, and and a three-beep dial tone when attempting to make any calls; although it is still showing the vodafone 3G carrier logo most of the time (i'm currently using a vodafone PAYG sim, which works fine in my old phone).
I have tried alternative sims on other networks, which show the network connection to two, three or four bars - in this case T-mobile), but again even then, I still get a three-beep dial-tone when attempting calls, even with this said signal.
I have attempted to check the IMEI number online to see if it's been blocked (although have no reason to think it would have been), and it's coming back as clear from what I can tell, so that shouldn't be an issue.
It's currently running the 3.1.2 OS and using the latest carrier setting of 5.1 from Vodafone (these were updated about a week or two before the whole problem started), so i'm a little stumped as to where the problem may lie, other than with the phone itself, obviously.
So does anybody have any light they can shed on this problem, please?