I am a happy owner of a Treo 180, I find the convergence PDA - phone extremly useful, but I have to admit your job seems like having climbed a mountain and missing to do the final step to the top.
The phone software miss some functionality common in all cell phones like:
1) easily accessible call history; I can use button-down but I don't see the name, or menu - option - y, awkward!
2) ability to memorize caller ID when I'm talking and a dialog box for this after call is completed. (Good implementation will ask me to create a new name or add the number to an already existent name in the fonebook)
3) managing numbers from/to phonebook and SIM memory is possible only through the quicklist, this is just nonsense. Desirable features will be:
-search of SIM numbers not present in fonebook, and add option
-direct add of number to SIM
4) option to set desired defaults:
-quicklist or keyboard or fonebook
-quicklist shows preset numbers or history or (WHY NOT?) most used numbers

All this will require few days work, I hope to see some implementation in future updates.

Thanks for your attention

Gianni Barberi