RCaddict,
steven r asked me to chime-in here since he knows I work for an alarm company.
He is quite correct about the "$100 Specials". They are akin to the "free cell phones", nothing but a ploy to get the salesman's foot in your door. Usually you find that the "deal" is inadequate for your needs and what will actually work for you is significantly more money down and more money a month. Not to mention the monitoring and / or maintenance contract that sticks you with a multi-year term, many of which self-renew (sometimes for several years at a time) if you don't send cancellation notice far enough in advance of their renewal date!
While several manufacturers
claim their alarm systems interface with X10, most do no more than what a X10 Powerflash module does.
Most alarm systems I have heard of are designed to communicate with a monitoring station which will require a monthly fee.
The only one I can think of, off the top of my head, that might meet all of your stated requirements is the Elk model M1 (brought to you by the same people as the Elk ESM1 X10 Signal Meter!). It has Voice Dialer capability and (with the addition of a PSC05 or equivalent PLC interface) can send X10 power line commands! You can find out about the M1 at:
http://www.elkproducts.com/. IMHO if you plan on spending the bucks anyway, the Elk M1 should make any self-respecting X10 DIY'er types drool until their socks are soaked!
P.S.
Before anyone asks, no, I haven't managed to get an Elk M1 to play with, but based on the information available, I certainly would if I could!