best way to get live ATC interaction on sim

[90cent]

I am working on my PPL and I can fly and land well but I am still rather weak on my radio calls and to reacting to some of the more non-standard ATC instructions.

What is the best flight sim program to just work on flying the 172 AND more importanty which program is best for working with ATC over the internet. How do I sign up to talk to ATC? I assume it would be an extra charge. Any info would be appreciated. Once I get this radio stuff down I will be good to go!!