Outlook/Outlook Express on the road

When users go out of state on business, what is the simplest way for them to access their email. Our local lan connects to a LOCAL ISP via DSL. I’ve setup an AOL account for a user to be able to connect to the internet and then used webmail, however, my users would like to be able to use their OUTLOOK or OUTLOOK EXPRESS to send/receive email. AOL does not support email with a 3rd party ISP. Do you know of any ISP that works directly with OUTLOOK?