A growing number of mobile operators are rolling out HD voice in their networks, allowing customers with compatible phones to make calls with better voice quality. The operators have been encouraged to invest in the technology by an increase in the number of compatible phone models, according to a report from the Global Mobile Suppliers Association (GSA).

The improved voice quality is possible thanks to Adaptive Multi-Rate Wideband (AMR-WB), a speech compression algorithm that doubles the range of voice frequencies transmitted, resulting in sound comparable to FM radio according to French operator Orange.

The technology has been a slow starter. Back in 2006 Ericsson and T-Mobile announced they had conducted the first trial of the technology in a commercial network. However, in the last couple of months the technology has started to take off, in large part thanks to Orange, which has been the biggest proponent so far.

Orange has launched Mobile HD Voice in seven of the countries where it operates networks: Moldova, France, Armenia, the UK, Spain (in the Catalonia region), Belgium and Egypt (in Cairo). In 2011, Orange subscribers in Switzerland, the rest of Egypt, Luxembourg and the Dominican Republic will also be able to make calls, according to the operator.

Other operators that have added HD voice in the last three months include SFR in France, Vipnet in Croatia, Tata DOCOMO in India and Megafon in Russia, according to GSA. Telstra in Australia and 3 in the UK, as well as a number of other unnamed operators, are testing the technology, GSA president Alan Hadden said.

The growing interest among operators is helped by the availability of more phones that can make and receive HD voice calls: for the technology to work, both parties to the call must use phones and networks that support AMR-WB, according to Hadden.

At first, the Nokia 6720c was the only phone that could offer the improved sound quality. However, Orange has now added the N8 and E5 from Nokia, the Samsung Omnia 7 and the HTC Desire HD to its line-up of compatible phones. The line-up also includes the 5230 and E72 from Nokia and Sony Ericsson's Elm, the company said.

The addition of more phones, in combination with increasing awareness among operators and more public demonstrations that allow users to hear the difference should help HD voice take off on larger scale, Hadden said.