Background The Optimus One and the Optimus T are essentially the same phone. The Optimus One is sold in most countries in the world. This has resulted in a huge number of Optimus One users in comparison to Optimus T users. This is reflected in the number of Optimus One ROMs available. There are a lot of great Optimus One ROMs. Problem The T-mobile wifi calling feature is only built into the T-mobile ROMS. This has meant that if you used a custom ROM based on the Optimus One you could not use the wifi calling feature. (Uses no minutes if you are on a plan and register for wifi calling) Solution Someone going by the name AxesofEvil has developed a zip file that you can flash over an Optimus One (P500) ROM and it will give you the ability to make wifi calls. It actually works!!! [MOD]Add Wifi Calling for froyo based roms (T-Mobile only) - xda-developers I hope this fix will encourage other Optimus T owners to explore all the great Optimus One custom ROMs!