T-Mobile vs. Sprint

Currently, I have a cell phone with two service providers. My reasons are simple. T-Mobile has my personal line that I've had for abot 6 or 7 years (maybe longer). It has a 773 area code and some pretty important features:

300 Anytime Minutes with MyFaves (unlimited nights/ weekends starting at 9pm)
Wi-Fi Calling (Permits calls on a wifi network without using anytime minsutes)
Unlimited Internet (Also allows me to use my phone as a modem for my laptop)
All the other basics (call waiting, voicemail, etc)

About 4 years ago, I got a second phone on my parents Sprint plan which allows me to communicate with my family in Arkansas using a 501 area code. With both plans, I am using a Blackberry- a Tour on Sprint and a Curve on T-Mobile.

Although Sprint does offer an very nice "all-inclusive" plan, its missing some essentials that I'm trying to determine the value of. For example, with my parents current plan, I can't use my phone as a modem. Sprint would force me to upgrade to a much more expensive plan and require me to add an additional service that would be add $50 a month to the bill. Also, they don't offer calling over the wifi network. They do, however, offer unlimited calling to any cell phone. Is it a worthy swap?

Finally, Sprint's international per minute calling is significantly more expensive that T-Mobile. On the other hand, I can't even have my T-Mobile phone turned on when I'm international or I get charged for a voicemail being left (even if I don't check it). Sprint also allows me to text (if texting works in the other country) unlimited back to the USA for free (using my unlimited text bundle).

So what should I do? I'm not concerned about the $200 early terminiation for T-Mobile and I'm desperate to get rid of this $80 a month cell bill. However, I am concerned about the features that I'll miss out on by leaving T-Mobile completely. Her are the alternatives that I'm considering:

(1) Purchasing a pay as you go wireless card.
(2) Paying per use for internet use at airports & hotels.
(3) Purchasing a 3rd party software that allows me to use my blackberry as a modem.
(4) Using the International SIM card that I already own when traveling intenationally
(5) Seeing how this new Vonage for Blackberry works.
(6) Relying soley on my magic jack.

Either of these options,and moving my 773 line to Sprint with my parents plan, would save me about $50 a month. That $$$ could be added to my IRA or to pay off some bill. I'm determined to make a decision before my next billing cycle with T-Mobile.