A decent deal. I have been using this phone for a month now. I am 80% satisfied with it. 20% unsatisfied because of the low ring tone/speaker volume and the good for nothing camera. I stopped taking pictures with this phone as I dont want to get disappointed seeing the results. Moreover, I tend to miss many calls due to the low ring tone volume. If these two issues do not bother you, then its an awesome gadget.
I am very happy that I can access my files in pdf, word and ppt formats when I am on the move.
I dont think lack of memory slot is a problem for this phone as you can always store what u need the most and you can always transfer to/from your PC whenever u want.
For 17, 500 I find it to be a good value for money deal as most of the other PDAs cost more than 23, 000. A780 seems to be bigger and bulkier than 768i.