3G modem and 4G modem.
A 3g modem is a terminal device for dialup. Also known as a Cellular Modem, Mobile Modem, Mobile IP Modem, Wireless Modem) A wireless adapter that connects a laptop computer or other device to a cellular telephone system for data transfer. Cellular modems, often contain their own antennas and plug into a PC Card slot, a serial port or into the USB port of the computer or other device. Cellular modems can operate on a variety of wireless data services such as GPRS, EDGE, UMTS, HSPDA, HSPUA, 1x and EV-DO.
A 4g modem is from tourth generation mobile communications technology. A somewhat vague term used to describe wireless mobile radio technologies that offer faster data rates than current 3G (third generation) technologies. 4G networks are also more data-centric and based on standard Internet technologies such as IP. Voice service is typically provided using a special form of VoIP. WiMAX and LTE are examples of 4G technologies. 4G LTE is most popular with 4G TDD LTE and FDD LTE.