The Whistle VOIP app recently received an upgrade. If you are a current customer, you would have received that same email also. What I like about this app is that it's Free to call anywhere in the continental US. So what if you have to wait 10-15 seconds after listening to an ad before your call is connected (That is how is stays free). While, I do not use it every day, it does come in handy, especially when I can save a few bucks on a long distance call or use it as a back up service.
One of their newest updated features, for a Limited Time though, is to use as many pushes as you want. There is also a bunch of other updates which you can see via the iTune Link below.