I want a cell phone that will work in US and mexico with reasonable
rates. Preferably aq feature rich phone such as treo 300-600.

Any GSM cell phone will do what you want, including the GSM version of
the Treo 600 and the Treo 270.

What will make it expensive or not is the carrier.  The cheapest way
to go is to get a separate SIM chip for the US and Mexico and swap
when you go from one to the other.  That way you can get domestic
rates in the US (with GSM providers like T-mobile, AT&T, and
Cingular), and domestic rates in Mexico with your carrier there,
without ever getting charged international rates.

Thank you. I assume you probaby mean change carriers entirely in
Mexico. I am really looking for a way tht wil allow me to cazll to and
from mexico cheaply. Right nw I have gone with a VOIP which is a
partially successful solution.