I got the AT&T 3G card with my Mini 10 but it's not usable. I'm using the Mini 10 outside the US, and have tried using it with both GSM and 3g 850/2100mhz networks and it will connect with both, and I'll be able to browse to maybe one website (download around 300KB) and then the connection stops working (it stays connected but no more data will transfer and I'll have to disconnect->reconnect). I've taken it to tech support who confirmed my APN and other settings are correct, and we have tested the SIMs using a USB WWAN dongle in my Mini 10 and it worked fine.
Seems like it is either a problem with the Connection Manager software or the hardware. Does anyone know of other connection software that will work with the card (I think it's a Sony Ericsson)?
Or any other suggestions for me to try?