The whole 4G LTE network situation is confusing because three carriers say they are running 4G LTE networks - AT&T, Verizon Wireless and MetroPCS - leading customers to ask the question, "Can I use my Verizon 4G LTE smartphone on the AT&T 4G LTE or MetroPCS networks?"
Verizon confirmed that you won't be able to use Verizon 4G LTE smartphones like the Samsung Droid Charge or Droid Bionic when AT&T launches its 4G LTE network. The phones won't work with MetroPCS' 4G LTE network either.
All LTE networks by AT&T, Verizon and MetroPCS use SIM cards. However, the networks use different frequencies. Verizon's network is mostly in the 746-787MHz band, while AT&T's will be primarily in 704-746MHz. MetroPCs 4G LTE network uses the 1700MHz band.
Another problem is that the phone uses different voice networks. Verizon and MetroPCS use CDMA networks while AT&T uses GSM networks.
Although an enterprising smartphone maker could make a 4G LTE device that runs on all networks, the cost would not be subsidized by the carriers.
A while back (6/28) MetroPCS was unlocking Verizon and Sprint CDMA phones to work on its network for voice use only; data did not work. We called our local MetroPCS store and was told that they will set up a "basic" phone to use on the MetroPCS network for voice only but not for a BlackBerry or Android smartphone. The rep would not reveal a price for the service over the phone.