Pro's using your Treo 750 vs. stand alone PND:
1) More flexible and easier to change to what ever mappoing software you like vs. you are locked in to only ONE GPS software provided in the PND.
2) Also, you could load other GPS software in addition to the street navigation software, such as Topo maps from Fugawi for out door activities such as geocaching, biking, hiking, and fishing! This is not possible with PND because you are not allow to install any additional software on to the device. If you like to take it with your for flying, just load up WingX or Anywhere map: http://www.anywheremap.com/. Any new GPS software introduce to the market, you are most likely able to enjoy / take advantage of them vs. if you are using a PND unit, which is pretty much in a LOCKED DOWN environment.
3) Travel lighter and battery last longer on the Bluetooth GPS receiver vs. PND. Bluetooth GPS operation time per full charge goes for 8 to 32 hrs depending on the model vs. 3-5 hours on the PND, plus PNDs are bigger and heavier to carry in general due to the larger screen size. If you will be using a navigator inside of your car, this may not be a concern at all.
4) (I my opinion), it helps reduce the chances of break in to your cars. When you leave your car, you automatically take your cellphone with you but I see most people tend to forget to remove their PND from the windshield pedestal and just leave it there.
Con's of using your Treo 650 vs. stand alone PND:
1) All the 4 points above plus below
2) Of course, larger LCD of up to 4.3'.
3) Dedicate unit for un-interrupted guidance. Some customer do not like when using their cell phone as a navigation device especially they are navigating in a complicated intersection and received a call. But if you have a Bluetooth headset connected to your phone, this will be a non-issue since you could accept the call and immediately bring back the navigation screen and follow the VISUAL prompts minus the voice prompts. Voice prompts on your phone will resume (on most software) as soon as you end the call.
NOTE: Speed of route calculation and re-route if you missed a turn should almost identical btw a decent PDA/Phone vs. a decent PND unit.
Please discuss this in our forum using this link: http://discussion.buygpsnow.com/forums/4773/ShowThread.aspx