"Sadly it was a simple phone switch.. So it has to be handset related. I switched from a Nexus One to a Razr. I can pop my SIM back into my old phone, and tethtering works fine. New phone and tethering doesn't work. All the APN's are entered correctly. I'm holding out hope that an Ice cream sandwich update will save me from throwing my razr out the window."
Its because its running 2.3.5 android which is made no avoid tethering, some versions depending on which carrier block access to the tethering menu in android. Other's allow it but block the connection to google (turning the connection from green = google connected to white = not google connected)
You can download apps like 1-click hotspot or tethering, I forget the exact name but they will give you access to the menu. Also you must have the "tethering APN"
This is absolutely correct. When I got my new corporate-provided Razr, running 2.3.5, turning on the hot spot would lock up the phone, forcing a cold reboot.
In prep for an upcoming road trip, I spent the day updating all my devices (laptop, rocketstick, razr, android tablet, iphone, digital camera, gps, etc), and my Razr updated to 2.3.6, and voila! tethering/hot spot works fine.
I posted this in another thread about HotSpot, solved my hotspot problem.
My plan already has tethering and after ICS update on my GNote tethering stopped working. It acts like it works, my tablet gets an IP address from my phone but it will not route traffic. I found a solution FoxFI