GPS turn by turn navigation does not require a 3G data connection. There are many downloadable navigation maps available. Look in the app store. TomTom, Garmin, Co-Pilot come to mind, but there are others, both free and pay for.
Your 3G iPad includes a GPS receiver. Just turn it on and use one of the turn by turn nav maps. I never used telenav but I believe that is a streaming map rather than a downloaded map. So with a streaming map you would require a 3G data connection while navigating. There is no need to stream a map.
Try downloading a map at home. You'll see it works the same as telenav except you won't get real time traffic updates, real time gas prices, real time weather, etc.