TL;DR: Buying a phone line seems to be more expensive than having the alarm monitored through the internet somehow. Alarm Relay seems like the cheapest option for Internet Monitoring.
Using a Phone Line
AT&T charges $35 a month for a phone line and Time Warner charges $39.95.
Total: Approximately $50 a month and $600 for a year.
Using The Internet
Can send e-mail based on alarm events.
Yearly Total: $315.40 (for a year of monitoring and the module)
Monthly Service Cost: $17.95 (module is $100 initially)
Alarm Relay says they do not support VOIP monitoring through the OOMA, and they say we will need to buy the internet monitoring module for $144.
Yearly Total: 251.44 (for a year of service and the $144 module)
Monthly Service Cost: $8.95
Requires $120 cellular communicator which would be specific to our current alarm system. We may be switching alarm systems soon, so buying expensive alarm specific equipment may be a bad idea.
Prepaid service will cost around $100 per year.
The monitoring service will cost $142.40 per year with Alarm Relay.
Total: ~$360+ depending on the prepaid phone service cost