T-Mobile is offering free WiFi access to T-Mobile phone customers on the weekends. There is no indication how long this promotion will last, perhaps it is simply a change to their customer support model which would be awesome. In any case, all you T-Mobile customers get your HotSpot on! This is just one more example of how T-Mobile is far ahead in customer service.
Click here for more information.
As a security reminder, nothing you do over an unencrypted wireless internet connection is secure. You should not send user ID's and passwords, for example, over a hotspot unless there is some encryption involved with the application you are using. If you do send information in clear text there are people looking for your connection and will pick off that user ID and password and have access to whatever you are accessing.
The ultimate solution is to use a VPN connection which encrypts everything sent over the connection. Unfortunately VPN's cost money for hardware and software and must be managed. There are free or nearly free vpn services available that you can use as well. So a word of advice: protect yourself.
Note: Thanks Adam!