The beauty of having an open platform is that you can largely operate without boundaries and without the restrictions imposed by some overlord. If you want to save your precious minutes each month, it might be a good idea to load up your newly acquired T-Mobile G1 with iSkoot for Skype. This is the first mobile VoIP application for Android smartphones.
In effect, you can make Skype-to-Skype calls right from your new smartphone. Unfortunately, you do use some data and some airtime if you use iSkoot, but at least you can save on the major long distance charges that you may otherwise incur. Local calls might not be so good.
For more information, check out the official page. And yes, iSkoot is free to download.