1xRTT is a data transmission system used on CDMA networks that allows for connetion speeds of up to a theoretical limit of 144kbps in most implementations. Real world usage is typically much slower, though, coming in at somewhere around 80kbps. 1xRTT is often referred to as a 2.5G technology like GPRS, though it is officially a 3G technology according to the ITU's IMT-2000 spec.
EV-DO
2.5G