Not just devices that need to be considered
Yes, you need a full alpha keyboard like a blackberry. The blackberry user interface works - not great but infinitely better than windows mobile.
However, for a small business using POP3, the problem needs looking at end to end.
a) you need an ISP that diverts suspected spam, not just labels it; very galling to pay for spam.
b) you need a mobile phone operator that can connect your POP3 account to the device - t-mobile couldn't do that for me.
c) you do need customer service from the phone operator, which in my experience rules out Orange.
d) windows mobile only synch's properly with exchange (EU please note), so you have to pay phone rates for POP3 emails, even if you have already received them on a desktop.
e) lightweight laptop with wi-fi may be a better solution for many, perhaps in conjunction with a U3 smart USB drive. GPRS card as an expensive alternative for when it is really necessary.