I was recently in a similar situation with my 770. I needed to get a new cell phone plan anyway, and started looking into combining the two devices. I wasn't especially enthusiastic about the 770, but it was a good deal, and it worked well enough when I needed it to.

I was able to get on sprint's $30 a month sero plan which included 500 minutes + unlimited evdo data (cheaper than my old cell plan without any data!) so I ended up with an HTC mogul, and was pleasantly surprised with its ability to combine all the devices I had. Sure, the screen on the nokia is much better, but the mogul is smaller and easier to carry around. the slide out keyboard that is very handy too. The GPS locks in about 5 seconds, and is very useful with google maps when I need to check traffic, or survey the area.

the htc user base is also pretty good, and I am currently running a custom modified ROM that improves performance and is lighter than the stock sprint rom.

I also have a mio c310 PNA, that uses the sirf III chip iirc. it also locks in about 5 seconds and has always worked very well - especially after unlocking it and installing some extra features and skins. I was actually able to install the exact same navigation software on the mogul, and it works flawlessly. So I am going to sell the mio as well (already sold the 770).

Having one device instead of 3 is pretty nice. though if I feel that I need something more substantial for web browsing (which I can tether to the mogul), I may look into nokia's next generation IT or a mini notebook of some sort. but for now, the mogul is a pretty good all-in-one device.