As smart phones become more prominent the wireless industry has discovered that the 3G network can't handle the necessary data load traffic. The big four (ATT, Verizon, Sprint and T-Mobile) are looking at 4G to help them cope with the mass use of data that is coming for users across United States.
A quick review, there are currently two different systems of 3G network. GSM which ATT and T-Mobile use for their network and CDMA which Verizon and Sprint use. This is the issue of why Apple has not yet released a Verizon enabled iPhone. It would require them to come up with a new chip set for the internal makings of the iPhone.
The next generation of Wireless networks also fall into two categories. LTE and WiMax. WiMax is the first network out of the gate and Sprint is offering it on their 4G phones (for example HTC EVO). However wireless companies around the world are now behind LTE because each tower covers a larger area than a WiMax tower. As of now 123 countries are putting their support behind the LTE network.
In the US, ATT, Verizon and T-Mobile are going to use LTE as their next generation network. This would again put Sprint at odds. As more mobile phone manufacturers are going to put their resources on LTE enabled phones.
It is suspected that once LTE is being fully deployed in the US (by 2012) Sprint may switch networks as well and adopt LTE as their next generation network.
At that point customers may begin seeing true price competition between cell phone providers.