I just looked up the taxes on the ooma phone and it's $5.88 per month, that's crazy seeing the magic jack is just $1.98 per month. It's still cheaper than a landline.
The taxes will vary by state. I pay only $3.76 per month. Here is a link which will show the cost for any zip code:
https://go.ooma.com/tax_calculator
MagicJack plus now costs $29.95 per year which is $2.50 per month unless you're willing to sign up with them for five years which is $19.95/month. That would be a bit risky seeing that new technology is always coming out and that any VOIP company may go out of business at any time. I wouldn't sign up for any service for five years.
The general consensus is that MagicJack Plus is indeed cheaper but Ooma uses better technology which provides higher quality and advanced features. Also many users report that MagicJack will automatically hang up your call after 1 hour and 30 minutes after which reconnection may be denied for some time. If you're a business and/or make a lot of phone calls also please be sure to read MagicJack's rules on "excessive service".
Before you get either it may be a good idea to read the customer reviews on Amazon to get an idea of what each service is like:

MagicJack Plus:
http://www.amazon.com/Improved-Magi...dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1
Ooma:
http://www.amazon.com/Ooma-Telo-Fre...dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1
Bottom line: If you're looking for the absolute cheapest service and are not too concerned about high quality, features, or support then MagicJack Plus is the least expensive option at the present time. If you want a very low cost service with superior quality, support, and advanced features then consider Ooma.
Other services to consider depending on your needs are Vonage, Obihai, Google Talk, and Skype. If you get good, reliable cell phone service at your house also consider dropping a land line altogether.
Now if you want to talk cell phone services, Consumer Cellular can save you a small fortune over Verizon, Sprint, and AT&T even with a smart phone and a data plan.