Currently, several carriers offer a 4G network service,
but these 4G networks either use enhanced
3G technologies or offer only a minimal implementation
of 4G technologies. The 3G networks
that have been extended to 4G are Wideband
Code Division Multiple Access (W-CDMA) and
WiMAX. W-CDMA evolved into HSPA+, which
AT&T currently uses. AT&T is also investing
heavily in LTE and LTE Advanced. WiMAX has
evolved into a 4G network and is used by Clearwire
and sold by Sprint. The 4G network that’s
running at low speeds is LTE, used by Verizon.