Sprint has turned on what is known as Modem NAI, a new tethering monitoring system in almost all Power Vision devices that will ensure that Power Vision phones have the required Phone-As-Modem plan to be able to connect to the internet
verizon has already done this, AFAIK it started with the 8100
so the 8100 8300 8500 8600 9800 9900 LG phones have this, and likely some other models
but it only affects using the EVDO network, puting the phone in 1xOnly mode for the 1x backdoor ( using minutes ) completely negates the EVDO NAI concern on the verizon network