Matthew from grack.com claim to have linux OS running on Treo 650.

Remember we reported that Palm is likely to build mobile phones using the Linux OS? This guy is in the way of runnning linux in Treo 650. Some of the questions he answered

1. Will the GSM radio work? Answer: Yep! The GSM radio is connected to a UART on the processor. You activate/dial it using GSM AT commands. There’s a couple of pins you need to activate to bring it up, but it won’t be hard to narrow them down.
2. Can I load it without destroying my phone? Answer: Yes. The current method for loading it uses the phone’s bootloader to place it in RAM . It doesn’t write any permanent data to the phone yet, and it’ll only be using the SD card for read/write operations anyways.
3. Will the CDMA radio work? Answer: Hopefully. Shadowmite pointed out that the CDMA radio uses AT commands as well. This means that a single phone program might be able to provide both GSM and CDMA service!

Visit the site at

http://www.grack.com/programming/misc/TreoLinux.html