If you are using AT&T as your carrier, or an AT&T MVNO (such as Straight Talk or Net 10), you might want to stop reading. I was a subscriber to Straight Talk and never got Internet Sharing to work on my Lumia. Proceed at your own risk of frustration.
This thread is intended to carefully document my experience getting Internet Sharing to work on my carrier unlocked Lumia 900.
If you wish to enable Internet Sharing:
- Call AT&T and ask for an unlock code. If you do not have a competitor SIM, you can produce the Unlock code prompt by dialing ##782# from the dialpad.
- Connect your phone to a PC and backup your photos, videos, and music. You'll be doing a Hard Reset soon.
- Remove the SIM and replace with a non AT&T SIM, such as T-Mobile.
- Perform a Hard (Factory) reset by going to Settings -> About -> More Info -> Reset.
- Perform the initial setup tasks using the advanced mode.
- Press and hold POWER to turn the phone off. After 30 seconds, turn phone back ON.
- After 1-2 minutes of the phone being powered on, be sure you have a data signal; verify this by opening a browser and navigating to a website.
- After verifying you have a data signal, attempt to enable Internet Sharing. Go to Settings -> Internet Sharing -> ON. The phone should show the Wait indicator for 5-10 seconds and then present the Wireless AP name, encryption type, and password. You can change these settings.
A word of warning: Do -not- install the Network Setup app. This will break Internet Tethering and lock your phone down tighter than Fort Knox. If for some reason install Network Setup out of curiosity (as I did), and break your tether, just do a hard reset and repeat the steps above (sans the AT&T unlock code entry business.) The Lumia should grab all the network setup data it needs from the inserted SIM at first boot. If you change SIMS, you'll need to do another hard reset; it is speculated that the LUMIA does not update network settings when a new SIM is inserted.