My SO just turned in her 3G phone to go back to a regular 2.5G phone with EDGE GPRS which is a big improvement over traditional GPRS speeds. I also use EDGE GPRS. 3G service in Taiwan is not without its reception problems for regular phone calls. It is a new network and the auto switchback to the GSM networks is not perfect. For Chunghwa and FarEasTone both have GPRS unlimited plans for 300 and 400 respectively.
Taiwan is offering free 3G cards if you switch now. You don’t have to get any 3G services. It’s always good to change your chip if they offer for free before you burn it and lose all your numbers and it costs nothing to get the chip.