Roamers can get a temporary ID via SMS: When visitors step into a SingTel hot spot, they can dial *186 on their cell phone and get a code with a user ID and password that gets them on the Wi-Fi network. They'll be charged for using the network on their cell phone bill.
In Europe, Excilan is offering a similar service. Users there input their phone number onto a gateway page which triggers the system to call their phone. Then the user approves the charge for Wi-Fi use on their cell phone bill.
These are great ideas that eliminate some of today's roaming/billing issues. It seems like we're pretty far behind Europe and Asia though and these arrangements probably take a bit of cooperation between cell phone and hotspot operators. Here, it seems that the two are just learning that if they work together they can all get a piece of a bigger pie. Plus, we don't use SMS quite as much as folks around the globe.