I have been looking ever since i purchaed my Blackberry Bold 9700 for a free turn by turn sat nav.http://vfuk.navigator.telmap.com/vfuk/
Copy this address into your phone's browser which gives you the software with no need of purchase. It is a Vodafone SatNav by Telmap. No signs of a trial, mine has been working since January and a freind of mine for a year now.
It also has traffic updates which comes in handy. This does use the internet to download the route so i will recommend you have an internet package.
Phone models it supports:
BlackBerry® Curve 8110 smatrphone
BlackBerry® Curve 8310 smatrphone
BlackBerry® Bold 9000 smartphone
BlackBerry® Bold 8900 smatrphone
I have not tried other models, however if you have the Blackberry 9700, select the 8900 and it works perfectly.
EDIT: Not only for Vodafone customers, you can be on any network.
This works fine with the nokia E51 too and an extrenal GPS