Take a look at two products from JDS Technologies.
http://www.jdstechnologies.com/The first is Stargate. It's a very powerfull system that integrates far more than just your X10 devices. Add the IRXpander and you have full two-way control of Ir devices as well. Also, all of Stargate's telephone functions (caller ID, voicemail, call screening, etc.) and the things that Robert mentioned. Stargate is definately the way to go if it fits your budget.
A cheaper option is the JDS Timecommander. The Timecommander is a scaled down version of Stargate (actually, it's vis versa but same difference). The TimeCommander handles all the X10 and, with the addition of the IRXpander, all the Ir stuff as well. What you're giving up is the telephone, voice responce, voicemail, etc. features. With Timecommander you also have the choice of going with (TimeCommander Plus) or without (TimeCommander) the hardwired inputs/outputs.
Approximate prices are as follows:
Stargate..............$933
Timecommander Plus....$590
Timecommander.........$295
IRXpander.............$230
Regards,
--LB