Back in December 2010, I wrote about how you can Activate internet tethering on Samsung Focus with Rogers Canada.
If you installed the latest WP7 update, Mango, this is still valid, but you have a new option: activate WiFi sharing!!
As for tethering, it is not built-in (hello Microsoft?) but here is how brilliant people save our lives!
Well, the procedure is not that easy, as you need to “interop unlock” your phone first, which will wipe your 3G, then apply a few more tweaks (update some registry keys) to enable 3G again, then deploy 2 more tools to unlock WiFi sharing and apply changes..
You can find the procedure there:
It is working for me with my Samsung Focus (v1) on Mango…. good luck!