With more and more people owning mobile phones and sat-navs, it was only a matter of time before the two converged. However, the technology is still taking baby steps and before you go shopping for a device that will make phone calls and direct you home at the same time, there are a couple of things to consider.

Right now the most common mobile phone/sat-nav solution is based on two pieces of hardware -- a Bluetooth GPS receiver and a mobile phone (we'll get to all-in-one devices in a minute). Before you can attach your phone to a Bluetooth receiver, you need to buy a memory card that's compatible with your phone and comes preloaded with sat-nav software and a map of your country. If this sounds like a lot of work, don't panic -- most sat-nav manufacturers sell the memory card and receiver as a bundle so you don't need to trek all around town.

Three of the most popular bundles are Route 66's Mobile 7, TomTom's Mobile 5 and CoPilot Live 6. These packages all come with the required software and Bluetooth GPS receiver included. Before you buy one it's worth making sure your phone is compatible, you can usually find this out on the company's Web site. Then you simply have to put the provided memory card into your phone, turn the Bluetooth receiver on and pair it with your phone. It's definitely not the easiest procedure, but it's a viable option for people who have a mobile phone and want a sat-nav. It's also not as expensive as buying a dedicated sat-nav which will cost around £100 more.

The other option is buying an all-in-one mobile phone with GPS but these are currently thin on the ground. Mio has just released the A701 that's a mobile phone with GPS support but it costs around £400 -- a little pricey if you just want it for weekends. There is a cheaper and more compact option called the Benefon Twig, costing around £300, but it won't be available until the end of the year. According to Benefon it features built-in GPS and has a dedicated button that takes you directly to the sat-nav application. It lets you tag a coordinate and then return to the same point later, and also has a 'Twig finder' service that lets you find other people with Twig phones.

The main problem with all these solutions is battery life. The battery on your mobile will drain very quickly due to the demands of the GPS receiver or a Bluetooth connection. The sat-nav application will typically run for around 2-3 hours, which isn't a long time if you're going sight-seeing or will be travelling for a while. You can get round this by using an AC adaptor or car adaptor, but this takes the 'mobile' out of your mobile phone. So before you part with your hard earned cash, Marcus, think about whether you really want a two-in-one or just two separate devices that are specifically designed for calls or navigation.