They deduct minutes to every call to voice mail. Google Voice and Skype seem to take out from the 300 too. You really can't talk with this plan. This is for data-centric use.
But the texting rates are much, much better than a traditional carrier.
But Android has sip clients. who needs voice?
Also there are plenty of skype apk patched to behave the same in wifi and 3g, meaning it will go via data no matter what