I'm having real trouble with my Google-fu today, for some reason, but anyway...I need to get a GSM modem for a server I'm running (in the US). It needs to connect via the serial port (i.e. not USB ...

You can save yourself money by leaving your SIM card at home and using a GSM-to-Skype bridge to take calls on your phone via WiFi. [Trax] is using a USB GSM modem to take cellphone calls on a PC.