InnoTab 3.5mm Uart
This procedure has been documented in a way that someone who has very little experience with soldering or board modification should be able to accomplish the mod. In addition the parts chosen have been selected due to the availability, ease of use, and cost.
Note: If you use a 2.5mm stereo socket instead of the 3.5mm one, you can use the many "Motorola T191" and compatible cables as they are used with OsmocomBB and a varity of other Osmocom projects. The cables are also often available cheaper than the 3.5mm cable from Digikey linked below.
NOTE: Sparkfun.com has a good selection of compatible parts