Sprint now has a plan that lets you use up to 50% of your peak minutes to roam off-network. You have to sign up at a store or by phone, you can't do it on the web site for some reason. The plan with roaming is called the "PCS Free and Clear America" plan. Their "Free and Clear" plan is only for their own network, which is smaller than Verizon or AT&T's network. If you don't often travel outside of Sprint coverage then it's okay to just pay for the occasional roaming (especially if you're on a low-priced Sprint retention plan).

Verizon lets you roam onto some of Sprint and Alltel as part of America's Choice, and also has the "National Single Rate" plan that lets you roam completely off-network.

AT&T doesn't let you roam onto other carriers on their "AT&T Wireless National Network" plan. This can be a problem as there are many areas of the country where AT&T does not have service, including some medium sized cities. There is always the Digital One Rate plan for those customers that need to go off-network a lot, but it is much more expensive.

Off-Network roaming can cost the provider a lot of money. This is why they tend to discourage it by making the off-network roaming plans so expensive, and by not including loads of off-peak minutes. They also don't allow people that don't live in their local coverage area to sign up for service.