While new technology often over-promises and under delivers, JOHN HARRIS discovers the unexpected benefit of the matrimonial harmony offered by satellite navigation devices.

Technology's greatest contribution to marital bliss, handheld satellite navigation, has finally reached the mobile phone.

During the past few months, mobile handsets equipped with GPS (Global Positioning System) technology have moved from executive indulgence to throwaway bait for a telco phone contract.

In November last year, I bought a $1299 HTC TYTN II handset that comes with the CoPilot GPS software. Last week. I ordered my wife a new Nokia 6110 Navigator, with the Route 66 GPS software, which was free on a two-year, $49 a month contract.

At a contract cost of $1176, the Nokia cost $24 less than the HTC handset - before counting bundled calls.

This downward pressure on prices is not surprising given the amount of choice in this market sector.  Other mobile phones equipped with GPS technology include the Nokia N95, the Blackberry Curve and the recently-announced Sony Ericsson Xperia X1phone.

I suspect one reason for the popularity of GPS is its relationship benefits. Any couple who has ever used a GPS unit to navigate an unknown city has learned firsthand the marital delight delivered by this technology:

Rather than squabble about directory directions, street signs and name pronunciations, both driver and passenger merely obey the instructions issued by the omniscient GPS unit - which an astute husband will have configured with a female voice.

However, not all GPS devices are created equal. Pureplay GPS units are equipped with a built-in GPS receiver that communicates directly with orbiting US Department of Defence GPS satellite. This is free to use.

Some handsets use a supplementary technology, called Assisted GPS (A-GPS) which finds your position through your carrier's data communication system, which can incur data charges.

Once affordability is dismissed as a barrier to buying, your choice of GPS phone comes down to size and performance.

Nokia's 6110 Navigator is a compact handset, weighing in at 125g with a 2.2" QVGA screen. The HTC TYTN II is a chunkier unit - with all the industrial design grace of a brick - at a hulking 190 grams and a 2.8'' touchscreen display.

Both devices provide voice-assisted direction to your destination although neither offers the convenience of actually naming streets.

Phone integration with GPS is very convenient: You can search for Points of Interest along a planned GPS route, such as a restaurant or motel, and then use your phone to call the listed PoI number to make a booking in advance.

However each unit has its quirks:  While the HTC accepts destinations in the standard GPS format - Suburb, then Street, then Number, the Nokia will accept street-only searches, but prefers the street number after the street name.

Also, remember that GPS devices are real power hogs: Don't expect to get a full eight hour working day from a handset if you're using it to find your way around town a lot.

Travelling overseas with your GPS phone also requires advance planning because you have to buy extra maps.

The Nokia's Route 66 software sells regional US maps at US$50 a pop, which quickly add up if you're visiting multiple areas.

The HTC's CoPilot software offers one map covering North America for $99, but my experience of actually getting this downloaded software to work has proved fruitless despite several months of email with CoPilot in the UK.

However the Australian maps pre-installed on both the Nokia and the HTC have already paid for themselves - and are considerably cheaper than marriage counselling!

First published in The Independent, Friday, May 9, 2008