I know from reading online that it's possible to switch out a sim card from a Sidekick for use on a Treo -- as long as you contact T-Mobile and ask them to switch your data plan from the Sidekick specific plan.

I'm planning on ordering a GSM 650 from the NY Roadshow. But since it won't ship for a while, I thought I could go ahead and get a free (after rebate) Sidekick from Amazon to use in the meantime and then switch the sim card when the Treo arrives.

Anyone has experience with T-Mobile's year-long contracts to know if I would run into any fees to switching my account over to a Treo (from a Sidekick)?