T-Mobile is claiming 4G speeds for parts of its 3G phone network. It’s billing the new T-Mobile HSPA+ network as a “super-fast mobile broadband network that delivers 4G speeds”.

The service is now available in the New York City metropolitan area, including New Jersey and Long Island, as well as Upstate New York (Albany, Buffalo, Rochester and Syracuse), Connecticut (Hartford, New Haven, Milford and Stamford), Providence, R.I., Memphis, Tennessee and Las Vegas. The “4G” phone network has been live for some time in Philadelphia and some parts of Washington, D.C.

T-Mobile says it will be expanding the HSPA+ network to cover Boston and more of Washington, D.C. in the coming weeks. The network offers theoretical peak download speeds of 21Mbps and is due to be available in 100 cities by the end of the year.