I recently put an O2 sim card in a T-Mobile phone.?

You may not unlock your mobile according to the appropriate network , When you originally buy your mobile it will be locked to a specific network i.e. it won’t work if you use a SIM card from a different network , you need to unlock it according t the network you reside , for that make use of the unlocking site , i got the unlock code here Mobile Unlock Solutions- Unlock Your Phone for unlocking my mobile under orange network & i unlocked my mobile safely . make use of unlock code & unlock it under orange network & gain solution at cheap cost . i hope this would be helpful for you ...