I've currently have a GSM phone on a voice-only plan from a local company. The n900 is really looking sweet, so I thought I might just by one and stick my SIM card in it and use it as a phone + WiFi internet tablet. This should work out pretty well sense I spend most of my time with WiFi coverage.

Can anyone think of any gotchas with that plan? The fact that I have voice service but no (mobile) data shouldn't be a problem right? What about the assisted GPS? Am I going to wait 5 minutes for an initial fix or does it use cell tower data that is available with voice-only service? Will the mapping/navigating work with no data connection (ie have at least the local maps cached via wifi)?

Any thoughts are welcome.

I may do this, myself. The times i need data access and am not around wi-fi are very few.

There are two kinds of things i've heard referred to as "assisted GPS". One is using cell tower triangulation to get a rough location. This is not really assisted, and not really GPS (literally, maybe, but it doesn't use GPS data at all). This doesn't require the GPS radio to be on. Assisted GPS is using the server to process the GPS data to speed the rate of attaining a fix, and will most likely require a data plan.

So, you should be able to get a rough location using tower positioning, but for actual navigation and GPS, you'll probably have to wait a few minutes.