At first time, both SIMs, nextel and the other carrier, if putted from the beginning there is no problem. But when trying to change the SIM, to use an other phone number or upgrading the SIM model.
It forces to erase private data.
Message says: "A new SIM card is being used. All private data must be cleared before you can continue"
If no option its selected it erases it, hate to do a backup to just change the SIM or imposible to change the SIM on the fly.
Its Rooted, so looking forward to edit any file and line in the db files to fix this problem.