It's truly true: T-Mobile's Wifi-Calling feature has been pulled up out of Vanilla Froyo runner G2 and plopped back down into the Nexus One. Now you can have all the fun all your fancy friends have been having, just so long as you're working with N1s on the T-Mobile network. Learn all about it, specifically the instructions on how to do it, here courtesy of XDA-developers member Rsotbiemrptson having teamed up with some helpful XDA Developers buddies.
In an attempt to fix a known issue that might pop up for you, user IntersectRaven has created a new kernel for this hack, getting rid of the issue of your Wifi turning off when the screen does -- download that here: http://www.mediafire.com/intersectRaven -- then, if after flashing you've got the same problems, attempt changing your setcpu screen off profile to 245min 384max. Take a peek at the original forum post and note how the Wifi calling is now working 100%, and how Myshkinbob is also to thank for research and creating of the PM FAST patch. Then take a look at the instructions for getting Wifi-Calling on your Nexus One here:
1. Download CyanogenMod 6.1.0 rom and copy to SD-Card (Not included)
2. Download the app from the first post or this one and copy to SD-Card
3. Download WiFi_Calling.zip and extract the contents to you SD-Card
4. Flash CyanogenMod 6.1.0 (Gapps is optional, It is included in my mod)
5. Go through the initial setup and sign in, then reboot to recovery
6. Flash WiFi Calling Kernel.zip, reboot, then reboot to recovery (It’s IntersectRaven’s kernel but can’t remember which date, fairly new though, that I have added kineto_gan.ko to)
7. Flash WiFi Calling Libs.zip, reboot (Includes libs from Evil’s Mytouch4G v.0.6 Rom, and a modded build.prop from a stock 2.2.1 rom)
8. Install MS-HTCVISION-KNT20-02.apk
9. Connect to WiFi
10. Open App and enable
Remember all of these files (or additional ways to get them) can be found in the original thread over at XDA Developers Forum.
[Via Android Police]