I have a i610 nextel and have tried placing my sim card into a 7510 it keeps telling me that I need to insert sim. I have tried this several times to no avail.
Although I have placed my wife's i730 card in the 7510 and it work fine. Does anyone know why this is not working????

There are a couple different SIM Cards for Nextel. Some work in the BB, some dont and some offer limited functions. Your 610 probally has a newer sim card that the 730.

Try searching this forum, there a dozen or so threads discussing this.