It looks like getting free data access on iDen handsets is going to end, likely on or before 6/20/10 according to this Sprint document (credit Engadget). Coincidentally, this is the same day that the Motorola i1 is released, the first Android phone on the iDen network. With this phone, Sprint would needed to lock down iDen data access a bit harder than blocking the phone’s built-in browser (the status quo), so the change will affect all phones on the iDen network (Boost and Nextel).
This also means that getting mobile connectivity for your Arduino will no longer be free. Boost mobile’s data rates run at $.35/day.
Update: 6/20 has passed, and I still have data access.