Sold a phone - buyer being prompted for password?

I sold an HTC Desire to someone on eBay. Before sale, I factory reset it, and tried my T-Mobile simcard to make sure it works, which it did.

New new user has put in his O2 simcard, but is being prompted for a text (not pattern lock) password. Any ideas? I've never put a password on that phone, so don't know what to recommend!

These issues over eBay are always very ugly business, especially when the phone sold for £70. Please help with any advice, if you can! Why is it asking for a password? Is it because a different simcard has been input? Is there any way the buyer can get it sorted?

Aren't android phones linked to google/gmail accounts? Maybe he needs to use yours (unlikely if factory reset although you put your sim card in) or his if he's got further than he said? (Thoughts based on you saying it's a text password as opposed to a numeric).

Does the prompt have a title i.e. 'sim lock' etc.

Can he not try a factory reset himself?

[ethariel]

Was the phone locked to your network when you got it, if so, it may need to be unlocked. The T-Mobile settings will in all likleyhood run on startup and not allow a connect to the o2 services unless 'unlocked'.

tho i may be wrong...