I don't like the APN-renaming method for toggling 3G. I've had problems with it. I have been using a free app named Llama
to toggle 3G (mobile data). Llama gives you the choice of toggling mobile data directly or using APN renaming.
To accomplish this, you create an "event" in Llama that simply turns mobile data on (or off), then go to a home screen and long press to create a shortcut, select Llama, then select that event. (You do not
go to the Applications screen from the "Select shortcut" screen and then select Llama; instead, you select Llama directly from the "Select shortcut" screen.)
On my Photon, this works great, and quickly. Llama does many, many other things as well (especially if your phone is rooted).