Which phone is a better phone for GPSing? the Treo 700p or Treo 700wx? Both verizon 

Neither, because of the smaller screen size of 240 x 240. If you have to stick with Treo phones, go with the Treo 750.

You should consider the bigger screen phones with built-in keyboard, such as

the Samsung SCH-i760

or the Wireless XV6800:

A few things. The price of the phones you listed above, even in contract, on ebay. Are to high of price. I can get a 700wx for 100 bucks average. And treos do have built in keyboards. Your looking at 300 bucks on ebay at least, for the xv6800. The xv6800's screen is a wide screen version of treos screen. 240x320.  Now you have moving parts (sliding keyboard), which only God knows some people CANT have. And they both run the same operating system. Theres a TON more features out their for the Treo compared to the xv6800. So...if the only thing I get is a longer/wider (how ever you wana look at it) screen, for 200 dollars more. O ok, the xv6800 has built in wifi. Ya I can add that for 40 bucks. So...if I all I get for the 6800 is a wider screen for 200 dollars more (used), 300 dollars (new), wifi, and bigger keyboard. I would have to say no.

Treo is 2.28x4.44x0.9 and the 6800 is 4.3x2.3x0.7, I can deal with the two tenths of an inch thicker

 Did verizon lock-out the ability to use the GPS with 3rd party apps (OnCourse Nav, TTN, Garmin), on the xv6800?

I am sorry but I do not have a solid answer on this. We all know you could use the phone's built-in GPS if you go with their Verizon navigator (hoping to get more revenue stream for data plan...)

Evidently, the device GPS receiver is locked down and you should check with Verizon if they plan to unlock the GPS so all other 3rd party GPS software could use it.