hi,
I recently got a T-Mobile Lumia 810 with the 2GB plan which does not include tethering. I was about to return it and get an android phone as having tethering is a make or break feature for me and I refuse to pay 15$ for it when I can enable it on any android with ease.
I know that Nokia has an app called "Access Point" which enables editing and addition of APNs but if you search store via your tmobile lumia 810 that app wont show up. I was able to sideload it tho by going to the Microsoft Windows Phone Store on the web on my pc and clicking on the 'manual download and install' which lets you save the app to your pc. I then copied the app to an SD card and inserted the SD card to my Lumia 810. You then goto Store on your phone, and choose SD card (it takes a few minutes for the app to register the SD card if u just plugged it in, at least it did for me) the downloade app will show up under 'Compatible Apps', I installed it from there and what happened was this: In the 'Settings', at the bottom, a new 'Access Point' appeared which let me choose Tmobile APN and set it. After I did that when I went to 'Internet Sharing' I was able to turn it out and setup my wifi hotspot and connect my PC and android phone to the Lumia 810's Internet!
What I do not know is if Tmobile will notice that im tethering and then charge me for the feature heh. Ill be sure to find out I guess.
Can also use this QR code to install the Access Point app from Nokia:
to scan it use the Search on the phone, click Vision icon and focus the code, a web url link should appear, click on it to install Nokia's Access Point.
Let me know how it goes for all!