Loopt is now available in the U.S. on Sprint, Verizon, Metro PCS, T-Mobile and Boost.

If you use Loopt on your AT&T phone, you can see updates from a friend using it on Sprint’s network, or on Verizon’s, and vice versa.

As far as platforms go, the circle is pretty much closed for mobile socnet Loopt

The location-based social network Loopt today launched its service in the Android Market.

Loopt®, an interoperable social-mapping and communication service, announced that its service is launching today to consumers through the Android Market, Google's new mobile application store.