If you travel frequently in the US and are willing to pay at least $70 a year, you should check out WorldMate Professional and Pocket Express Travel Edition.

Both programs, designed to provide assistance to such people, were reviewed by Phil Baker of The Daily Transcript:

Of the two products, Pocket Express Travel Edition is my clear preference. It's a better value and it provides more tools for solving problems that travelers typically encounter. And if you use a Treo it's your only choice.

The two apps, which provide useful utilities for travelers such as conversion, flight times listing, etc., work on most smartphones, including S60, Windows Mobile, Blackberry and Palm. They also require data access, the cost of which is included in the annual fee. WorldMate focuses on frequent flyers, while Pocket Express offers more comprehensive features, depending on how much you pay per year.