I don't want to discuss what I did and how many times (20+) with the new iPhone 5 during the 4 days trying to re-activate (Reset All Settings, Erase All Content and Settings, ...) with no luck -
voice activates fine but the data won't...
There is the ONLY one thing to activate your iPhone 5 (voice and especially data) is to get the original iPhone with the ORIGINAL sim-card inside the device from Sprint for now (until the day 10/5/2012 for sure)
(no other replacements from the Apple, sim-cards from Sprint even the new ones won't activate your iPhone's data). Until Sprint fixed this problem!
Swap the iPhone for the new one - no luck; Swap the sim-card - no luck, even the Sprint reps change IMEI and ICCID on your account - looks like the bug on there system (or so).
Go to the Sprint store (not the Apple!), change your device for the new one and you good to go after the couple of minutes activation!