Big difference in those 2. One being a BB and the other a Treo.
Pearl from T-Mobile is a GSM device. Unlocked version can be used on Cingular or used in most European countris, if you should travel there. Coverage is not as good as Cingular however. Palm is a CDMA device and can be used only on the Sprint network in the US. Sprint coverage is probably worse than T-MO. Verizon provides the second best coverage in the US, second to Cingular, and is the best CDMA carrier, in terms of coverages.
Pearl has the SureType keyboard which some say is not advantageous to a lot of typing. Palm has the QWERTY which IMHO is easier to type.
Pearl has the BB O/S which is up to date and very bullet proof. Treo has the Palm O/S which I consider to be old and in need of refreshing. It is also prone to frequent crashes and reboots.
You really need to look at the carrier you plan to go with and look at reception where you will use the device - live, work, travel, play, etc., then pick the phone you want.
