I’m installing a Linux server in a remote location where only dial-up access is available. The server runs Xubuntu 6.10 and will be used to capture weather data. It will run 24/7 and must periodically upload data to a website. First things first, I needed to get my PCI modem working. This can be tricky with Linux, but my Intel536-based model actually works a treat. The best place to start (with Ubuntu at least) is https://help.ubuntu.com/community/DialupModemHowto
NOTE that for Ubuntu 6.10 the current driver source from Intel does not compile. Thankfully, this is a semi-open source driver and someone has patched the driver code. Details are given at the link above.
Dial On Demand (DOD)
What I needed was dial-on-demand internet access. This excellent page provided all the info: