About 6-8 months ago I picked up a Samsung Series 7 slate, and a mail-in promotion for a free Omnia W. Under Vodafone I was happily using the Omnia W for (extremely conservative) browsing via Wifi net sharing.
When I switched to 2degrees, it turns out there's no automatic APN settings so I put in a custom APN, which worked fine for the phone itself to connect. However, when I try and activate Internet Sharing it says "Cellular data connection not shared." and says there is none, and I should check settings and signal. From a bit of searching on the net, I found similar issues with other WP7 devices in the states. It seems to me that unless you're using a Nokia WP7 device (apparently Nokia made an APN config utility), you can't share a non-automatic APN.
Anybody got any ideas? For now I'm using my Galaxy Tab (original), but it's not convenient at all especially with an Omnia W and a Slate 7 taking both of it's jobs.