Small independent carshare organizations like Autoshare generally have good-will based agreements with each other, so that travelling members can access cars in other cities. I live in Vancouver and I signed up with Autoshare for free under this kind of "roaming" arrangement. I pay a membership fee here in Vancouver, I shouldn't have to pay it anywhere else.
Lo and behold, one year later, I'm asked to pay a yearly fee, just like any other local Autoshare member. I was never informed that this would be for one year only. . .
Bottom line, if you're looking for hassle free roaming to other cities, go for Zipcar.