Just get Ooma
http://www.ooma.com/
After buying the unit, you only pay local taxes and fees. Mainly, this is for 911 service.
For my area the break down of cost per month is:
Regulatory Compliance Fee $1.59
911 Service Fee $1.59
Federal Universal Service Charge $0.29
State and local taxes, fees and surcharges $0.00
Total: $3.47
Tax calculator
Also, I think Ooma is the only voip system that supports fax. But that was from a brief research a while ago.
EDIT: both support 911
Further reading suggest that the 911 service on Magic Jack is not in compliance with paying the 911 fee. This may result in you having to pay an 1.59 or more later. Additionally, if you take the $20 per year and divide by 12, you end up with $1.66... what fees are they paying and how much is going into their hands per year? Are they even paying the federal or regulatory compliance fee?
Also on the note of 911. both options are not guaranteed to have the federal requirement of must function '99.9% of the time under all situations such as power outages.'.. much like your cell phone. So if you can live with this, I wouldn't worry about using Voip 911 services.