Telstra's new mobile broadband network is now ready for use, but limited to a five-kilometre radius around central business districts and airports.

Telstra this morning announced it will start selling mobile broadband modems for its new 4G network, also known as long-term evoultion technology or LTE.

Telstra has launched its 4G network, boasting data transfer speeds 25 times faster than its 3G network.

The modems, which are also known as dongles, will work at faster speeds inside the 4G network and revert to the 3G network in other areas.

The network has been under construction since May and is now available in the centre of capital cities, airports and some regional areas.