Hi Nicole,
Basically we wanted to use out ERP system on the handheld device. Currently we use SAP, so the only easiest way for us to do this is via the Internet. We configured the SAP servers with an Internet transaction server so that similar functions were available on the iPaq as on normal desktops. With the iPaq, we bought the compact flash jacket and a Xircom CompactCard GSM so that we can connect the Nokia 5110 and 6110 mobile phones to it. We then configured the built in web browser on the iPaq with the modem (very easy) and connect to SAP. The cost of the GSM card was only about £60, and the Compact Flash Jacket was about £30. The speed isn't terribly fast, but it is bearable. When phone companies data capabilities advance over the next year, the modem will already be able to cope with 24400bps speeds, which is enough for running a few transactions over the web.
I hope I have helped you, and please feel free to ask me any questions.
Regards
Darren