Any LG Black Experts Around?

My son was using an LG Optimus One up until last Monday, however it developed a fault and T-Mobile asked us to return it, which we did.

I explained that he was off back to uni last Friday, so wanted to make sure he had a phone to take with him. As they wanted me to return the faulty one before they gave me a replacement, I said I would take out another contract which I did. This time they offered to send me an HTC Desire. That phone arrived on Wed morning last week. Would you believe it if I told you, that there was a software issue with this phone and that had to be sent back too!!! This time they offered to send me another phone, and was offered an LG Black.

That arrived on Friday morning, just in time for my son to go to uni. He used the sim card from the faulty LG Optimus in his LG Black and it worked fine all weekend up, until last night.

Today he tells me that he couldn't send or receive texts, nor could he ring out on it.

I rang T-Mobile tonight and explained the situation and that my son lives 5 hours away from home. The female who I spoke to said she would ring him direct and speak to him. He went outside to take her call and stood outside for half an hour, only for her not to ring him!!

I rang them again at 8.30 and a male said he would ring him there and then. So apparently this male has done some resets and told him to go outside in half an hour and try it again.

He's just came on MSN and said that it's still not working.

So, can someone please tell me if it might be because he's been using his old sim from his faulty LG Optimus One in the LG Black, even though they're both T-Mobile phones?

Thanks,
Sal