Satellite phone users are for the first time being offered a way to make encrypted phone calls without having to buy expensive satellite-only handsets.

The new capability comes from VoIP call encryption company Cellcrypt, which has upgraded its standard client software for Blackberry and Nokia S60 smartphones so they can now make calls through Immarsat's range of BGAN (Broadband Global Area Network) devices.

Called Cellcrypt Mobile for Satellite, the connection to the BGAN is made using Wi-Fi, but otherwise the service is said to require no specific setup for the Immarsat service. As with Cellcrypt's GSM encryption, the only other requirement for a secure call is to have the same software running on the receiving handset, though unencrypted calls can be made to any receiver.

According to Cellcrypt's CEO, Simon Bransfield-Garth, the current market for fully secure satellite calls has hitherto been tiny, mostly users in the military and government.

"This space hasn't been well served up to now," said Bransfield-Garth. "The challenge has been to optimise the GSM so you get something like an ordinary phone call on the satellite network."

The company had had to take into account that satellite calls were prone to high latency as signals moved to and from satellites, which could reach several seconds in some cases. Bandwidth was also constrained. The company estimates performance as around a one second delay using a single handset and BGAN, or two seconds for calling a second handset also connected to a satellite terminal.

Cellcrypt plans to promote cost savings as another angle, undercutting conventional satellite call charges at around 40 pence (66 cents) per minute.

The main benefit for the sorts of specialist business users who would be attracted to the service was simply the convenience of being able to make satellite calls using the same handset they used to make any other call, said Bransfield-Garth. He saw it gaining traction in industries such as oil exploration, maritime, disaster recovery and possibly even some parts of the media.

The company has submitted Cellcrypt Mobile to the US government for FIPS 140-2 certification.