Is the GPS truly standalone?

If you do not enable GPS service on ATT, will it work?

If you had no SIM in it would it work with onboard maps?

Would it failover to Nokia's A-GPS if you had not ATT GPS enabled?

I have ATT and have never done GPS via phone.

Obviously a hand held Garmin GPS doesn't need phone service. Can the N900 do this as well in some fashion?