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.