Actually, it appears that the A300 _does_ support SDIO... according to this page on Sharp Japan's zaurus support page:
http://support.ezaurus.com/kyotsu/sl/cardphs_sl.asp... the AH-S101S SD AirH" modem can be used with the A300.
The whole no-SDIO issue on the Z models appears to be a driver issue, not a wiring issue. While this SD modem is not listed as being supported on the C series, as someone else mentioned in another post, a company is working on support for a SD WiFi card for the Cs.
I also _vaguely_ remember something about a jacket being available for the A300... maybe a CF jacket? Not too sure about that one, though.
The A300 would be a decent machine, especially since it can be bought really cheap here in Japan, but the screen is not very good, at least not when compared to the C series. I don't know how it fares outside, though... not sure what type of screen it is.
- ashikase