T-Mobile's venture capital arm T-Ventures has put money into femtocell maker Ubiquisys, and the operator says it plans to run a trial of the indoor basestation technology. T-Mobile is following rival operator O2, which announced a femto trial with Ubiquisys at the Mobile World Congress last month.

Femtocells are consumer devices which deliver 3G access in a building, and connect to the mobile network over broadband, improving indoor coverage and offering cheaper calls and better data traffic while indoors. Currently, the devices are being tested in operators' labs, with user trials expected from the end of 2008.

T-Mobile would not say how big its investment is - the cash follows similar investment by Google and others. Ubiquisys also provides femtocell technology for Nokia Siemens and NEC.

"As we move to future networks, femtocells will play a day one role," said Will Franks, chief technology officer and founder of Ubiqisys. Femtos will make good the deficiencies of today's 3G networks, but they will be in on the ground floor of future networks such as WiMax and LTE, he said.

At present there is very little being said in public about operators' lab trials, explained Franks. These will be followed by still-secretive "very friendly user" trials, where people who work for an operator get femtos to try at home, and then "friendly user" trials where real consumers get to try the technology. Finally, a "soft launch", and then a "hard launch will make the technology commercial, sometime around the end of 2008, he said.

While O2 and T-Mobile are making very positive noises about trials in the UK, the first femtos in the wild will be in Asia, and the first ones in Europe will probably not be in the UK, he said.