Employees could be offered smartphones for secure VoIP calls over WiFi and GPRS giving them a single handset and phone number for inside the office and outside.

That's according to network developer Allied Telesyn, which has just announced client software for WiFi-enabled smartphones. The company is initially offering Windows Mobile software - but a Symbian version is earmarked for later this year - that turns a mobile phone into a VoIP handset.

Allied Telesyn's senior VP of marketing Melvyn Wray said the software includes least-cost routing capabilities to detect and connect to a usable WiFi network as a VoIP client.

If there is no WiFi but GPRS is available, it uses a lightweight VPN routing technology called TenQ to link back to HQ, thereby remaining on the network as an IP handset with your normal internal extension number. Failing that, it drops back to dial-up GSM.

"This is telephone nirvana," claimed Wray. "VoIP alone does not address the fundamental issues of cellphone use - the ideal would be for each employee to have one phone for anywhere in the world, containing the complete company phone list, updated automatically."

Unlike some rival approaches to cellular/WiFi convergence, Allied Telesyn retains the smartphone as a VoIP handset outside the office. Wray acknowledged that mobile operators might not like this: "I can see that there may be some push-back," he said.

"But even a two-stage version, using WiFi in the office and GSM outside, could save a lot of money."

The smartphone client ties into Allied Telesyn's new VioCall Professional platform for voice networking. VioCall Professional works with any PC or telephony hardware, and comprises Windows client software plus an IP telephony server.

Phil Jopa, Allied Telesyn's CTO, said that one of VioCall's strengths is its ability to interoperate with other software, in particular MS-Outlook, so it could for example automatically re-route your calls to a colleague when you have a meeting scheduled.

Jopa said it supports presence too, and because it is SIP-based, "You can use SIP trunking services to replace traditional access methods, or a media gateway to connect to the PSTN - service providers need to look at embedding SIP into their networks."

Because VioCall is unified comms, anything you do on your PC is immediately mirrored on your IP phone, Jopa added. You can record a voice call with a single click on the PC, he said, plus it supports video and call recording across subnets.

He said that while VioCall Professional is aimed at companies with 50-30,000 users, versions for SMEs and service providers are on the way as well.

The IP telephony also uses another new Allied Telesyn technology called TenQ. This is a secure VPN with a very low set-up overhead, and a fast handover scheme built on the Mobile IP standards, the company claimed.

TenQ authenticates both ways, so the network authenticates to the client as well as vice versa, which could help block some security attacks. It uses keys downloaded to the client - TenQ software is available for Windows, Mac and Windows Mobile.

Melvyn Wray said that TenQ's low overhead - potentially just three packets - means that it can be used to maintain a connection over GPRS without much additional traffic cost.

He said that the TenQ range also includes wireless Ethernet routers capable of maintaining a broadband connection at speeds of up to 360km/h - Allied Telesyn has installed systems in the Far East to provide broadband to trains, for example.