I just purchased a Samsung Exhibit from a seller on eBay. The phone itself works beautifully. However, whenever I try to make a call or send a text, all I get is a message saying "Not Registered on Network." I have searched everywhere for a solution to my problem, but whenever I find something that looks promising, it isn't ever solved. Here is what I have done: 1. Tried it with 2 different SIM cards that work in other phones. 2. Took it to T-Mobile store and had my SIM card replaced 3. Factory Reset (a few times now) 4. Talked to T-Mobile support via chat - nothing. 5. Talked to T-Mobile support via phone - nothing. The phone does recognize that the SIM card is there. However, it just can't use it to get onto the network. Like I said, I searched the internet a lot for a solution, but I just can't find anything at all. Has anybody found a solution?!?!? Thanks in advance!