I'm a bit confused. Your Nokia is going to be the WiFi Access Point using the software you name. If thats the case your HTC should see it as any other WiFi (such as either your home router or the free WiFi in McDoalds). So why do you wish to use Ad-hoc? Or does the Nokia software only offer ad-hoc?
In my case I use my Android phone to WiFi Tether to my Android Tablet so that I can use my data allowance on my phone to power the Tablet. This can be achieved without rooting the phone (or in iPhone speak - Jailbreak). I see your example as equivalent with your (Nokia) phone in place of my (Android) phone. As the WiFi Tether App runs on the phone I don't need any additional App on the Tablet (equivalent to your Sat Nav) and the phone connects directly with my Tablets standard Infrastructure WiFi.
Or am I misunderstanding your question?