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After initial good impressions with the Sygic SatNav app I've now come to the conclusion that everyone who has said the iPhone has a poor GPS receiver is right!

I have also tried the demo of the Navigon app and found the same problem of 'lag', it does help slightly if I mount the iPhone on the windscreen as opposed to near the centre console but it still isn't right.

TomTom obviously know alot about SatNav and they realised that the iPhones built-in GPS was too poor to be reliable which is why they are releasing a cradle with built in antenna.

Surely then it's possible to use external GPS antennas with the iPhone, so why don't other companies release similar cradles with their software?

What I would prefer is a combined charge/antenna lead which plugs into the bottom of my iPhone and one lead goes to the cigarette lighter socket, preferably via a usb connection so I can use other plugs, and the other cable has an external antenna which can be stuck onto the windscreen.

This would mean I could mount my iphone near my centre console and just have a small unobtrusive antenna on the windscreen which would not obstruct my view.

Has anyone seen anything like this?