T-Mobile and 3 have gone head-to-head in the increasingly lucrative USB dongle market since T-Mobile cut prices last month.
Both companies have been overwhelmed by sales of the devices, which plug into laptops to give wireless broadband-speed internet access.
Vodafone is also believed to be selling large numbers of its own USB dongle, focusing on the business market.
The success of USB modems has been credited to the huge numbers of workers and students in temporary accommodation, especially in big cities.
A 3 spokeswoman said: ‘Sales for the USB modem have been strong and we are happy with the level of interest. We have just added another dongle supplier, ZTE, to help us meet consumer demand. At £10 for 1GB per month, our price plan remains the most competitive in the market.’
Carphone Warehouse is selling both T-Mobile and 3 versions, with several staff claiming sales of USB dongles are ‘incremental’ to fixed-line broadband.
‘It’s a different type of customer,’ said one Carphone staffer. ‘There’s a lot of people who don’t want to set up a fixed line in their home, or have had bad experiences with broadband.’
Prepay versions are available on T-Mobile and 3, although both networks are trying to push 24-month agreements.
T-Mobile’s service is the more expensive of the two, despite cutting its prices since 3 entered the market. T-Mobile claims it has a faster service, whereas 3 says it has broader 3G coverage.
A T-Mobile spokeswoman said: ‘We know consumers value the flexibility of mobile broadband, accessing the internet for all the reasons they love, whenever they want, wherever they are.’
Dealers have been keen to sell the USB dongles, but complain that commissions for selling them are too low.