Do they have an app that converts currency (into US dollars)?
iPhone has about 18 of them.
As for blackberry, the first Google result gave me XE Currency App for BlackBerry, a free one.
The Wolfram Alpha app does this and about a billion other useful things, like calculating the caloric content of a cubic light year of butter. If the $2 app is too much, you can just bookmark the website.
Google’s website itself does it. Typing “4 pounds in dollars” into the google bar on Safari on my iphone comes up with “4 British pounds = 6.2672 U.S. dollars”.