My friend switched her phone on as normal this morning, and it kept asking her to put the sim card in - even though it was already in, and it's been working fine for months now... 
We have tried taking it out and putting it back in, still nothing. We have put other sim cards in the phone, and they work okay, so we're guessing there is a problem with the sim card? She is working until later this afternoon and we're taking it into the shop then, but I just wondered if anyone on here knew what the problem may be, and how they may fix it? Also, will she be given a replacement phone if it needs to be sent away to be fixed?
She's on a T-Mobile Flext contract.
Thanks.

We have tried taking it out and putting it back in, still nothing. We have put other sim cards in the phone, and they work okay, so we're guessing there is a problem with the sim card? She is working until later this afternoon and we're taking it into the shop then, but I just wondered if anyone on here knew what the problem may be, and how they may fix it? Also, will she be given a replacement phone if it needs to be sent away to be fixed?
She's on a T-Mobile Flext contract.
Thanks.