[Nokia Lumia 900] patrick.l.vogt:
Trying to replicate steps outlined, with no success.

== EDIT == : For no explanation, I tried enabling Internet Tethering and it is now working with T-Mobile. I can't think of why it wasn't working 15 minutes ago.

Good Evening,

I am a noob. I've looked in the Lumia 900 forums under the terms Internet Sharing and Tethering. This seems to be the most active thread. I'd like to post my experiences with you here, especially because there seems to be indication that tethering is possible with an AT&T branded phone that is SIM unlocked.

My interest in tethering (or Internet Sharing) has been re-ignited due to the recent carrier unlocking and change to T-Mobile. I come from Straight Talk's $45/mo. unlimited 3g, which runs on AT&T's network. This is why I didn't need an unlock code until now. Ever since getting this Lumia 900, I have longed for JoikuSpot, the app I used on my Symbian Nokia e71. Alas, it was not to be. There are quite a few things I like about this phone, but the inability to tether adds a sour note.

I recently had AT&T give me an unlock code and promptly started with T-Mobile's $30 unlimited LTE plan. Internet tethering on this phone has been so confounding. After some research, I am going to come out and say it: it seems that tether enablement is determined by the phone's firmware and a call to the AT&T server - not settings on a SIM card.

With the phone SIM unlocked, I did a full reset. I attempted to access the browser to confirm Internet connectivity. When I go to activate Internet Sharing, I receive the same AT&T message about tethering. One difference I note is that it takes much longer for the message to display. With a Straight Talk SIM, the message displays in less than a second. With a T Mobile SIM, it takes about 5 seconds.

I have read elsewhere that when you toggle the tether switch, the phone pings AT&T's server to check your account and verify tethering is on the account. If a positive value isn't returned, the phone displays the "connection not shared" message. If you don't have an account with AT&T, a positive value can't be returned, so it's off by default no matter the carrier. It seems to me that with this version of firmware, tethering can only be enabled with AT&T's blessing. This would be the most logical explanation as to why tethering is not working even when using another carrier's SIM.

Unfortunately, it seems logic not present for this issue - there are at least two people on this thread reporting tethering working with an update through Zune. Then, if you even so much as install or launch Network Setup, you're hosed. Doesn't make any sense.

I have tried everything - messing with APN settings (before the hard reset), flashing another carrier's firmware using care center (which fails - I can only flash AT&T firmware!!), and doing a hard reset. I'm bummed that I did a hard reset and nothing positive came of it.

At this point, I'm trying to put these matters to bed:

Can a carrier unlocked AT&T branded Lumia 900 with AT&T firmware use Internet Sharing with another carrier in the US?

Can an AT&T branded phone be flashed to a firmware of a carrier that doesn't have these restrictions, such as Telcel?

Where can I get one of these flash boxes? I've been on the vendor's website and there's no way to direct order.

I'm especially interested in an update from T-Mobilers. Is your Internet Sharing still working?