Honestly, PUBLIC wireless is not that prevalent in the US. You will be able to get it in certain places such as airports, libraries, etc. It is pretty prevalent on college campuses, though, so living in Austin might be helpful in that you might get it often enough. But, you can't rely on much because a lot of places that have wireless require you to have a password to get on the wireless. It really depends.
Minutes are the number of minutes you use when you are on the phone. Let's say I had a phone convo with a friend that was 32 minutes and 30 seconds long, that would be 32.5 minutes. However, most phone companies have free nights and weekends at this point, so no matter how long you talk on the phone it doesn't count towards your monthly "minutes". Also, a lot of phone companies have free minutes if you are talking to someone with the same provider (i.e. Verizon). These are all important things to consider when you are getting a phone plan. If you are going to be calling home a lot, though, you will want to look at the International Phone plans and see how they work their minutes/costs. I am sure some companies are much better in this regard than others. I went abroad for 4 months a year ago and Verizon had a plan that was pretty cheap for my mom to get when she called me but I don't remember details...Sorry!
Hope this helps at least a little!