Don't be thrown by the complexities of all the different Wi-Fi pricing models. It's not really as complicated as it may seem.
As a practical matter, the first time you use a Wi-Fi hotspot, you'll probably take advantage of a promotional offer, or buy one-time (or pay as you go) access. It's a good idea to stay uncommitted for a while, and to try a variety of different networks.
So start with one-off usage, and get a feel for a number of the Wi-Fi hotspot networks. You should make note of locations, access speeds, and how good the customer service is.
After you've used a number of Wi-Fi hotspots, you should begin to get the sense of your usage patterns, and you may be ready to sign up for an extended payment plan by the month ...