U.K. start up Ubiquisys has rolled out a portable cell phone signal - dubbed the attocell - that allows people travelling abroad to make and receive calls as if in their home country.

According to the Google-backed company, the new smartphone accessory - a personal femtocell for the iPhone - works with any 3G phone and has also been tested with Blackberry, Nokia and Android smartphones.

Femtocells are low-power wireless base stations, providing 3G coverage for cell phones and route the calls through the Internet.

Ubiquisys, which develops 3G and LTE intelligent cells, says in a blog post that the world’s first attocell doesn’t incur roaming charges because the phone is not roaming, and does not connect to the visiting country’s networks. Instead it travels over the internet to the home country.

The company says the device with a range so tiny connects to a user’s laptop via USB that provides power and an internet connection. The device then analyses the IP address and radio environment to determine which country it is in, and sets its 3G radio power accordingly to below the licenced level. In some countries its range will be just 5 millimeters, in other countries, it could cover a whole room.

In 5mm mode, the traveller simply lays the iPhone on top of the device to enable an automatic connection and calls can be made using a Bluetooth or wired headset , or by using the iPhone’s speaker.

The attocell continuously monitors its radio environment to ensure that there is zero impact on existing mobile networks, says Ubiquisys. This, combined with its tiny power output, is likely to make the attocell exempt from regulatory controls and the requirement for type approval.

The device is the first to offer coverage for international travelers, though wireless network operators including AT&T, Sprint Nextel, Verizon Wireless and Vodafone have already launched their femtocell services.

Formed in 2004, Ubiquisys rolled out the first residential femtocell for less than $100 in December 2009. The company's other investors include tier 1 VCs and T-Mobile. The company counts Nokia Siemens Networks, NEC and Ericsson among its engagement partners.

The attocell innovation is a direct response to meet a specific requirement from mobile operators, says Ubiquisys chief executive Chris Gilbert.

A study from ABI Research forecasts that by 2011 there will be 102 million users of femtocell products on 32 million access points worldwide.

Already in the US, femtocells outnumber outdoor cell towers, with subscribers installing these plug-and-play access points to greatly improve wireless coverage in their homes and offices, says Simon Saunders, chairman of the Femto Forum. And, while coverage is a key benefit, there are a variety of other advantages that femtocells enable including improved battery life and faster data speeds that will allow for advanced consumer applications and services.

Ubiquisys says it will showcase the attocell at next month's Mobile World Congress in Barcelona.