Some of you are right to an extent... but dind't go into depth
1. If you flashed with MR1 you need to read on how to revert back to previous settings
here.
2. You do not need a data plan for standalone GPS. But,if you plan on using aGPS, which was the advice MrObvious gave you, then you need a data plan, or be on pay-as-you go, but you will get a few dollars in KB usage.
3. You can connect using no internet connection, with Standalone GPS, which takes longer.