Out of Office Internet Connection

We have an NT 4.o network with Exch 5.5 sp3 running OWA. OWA works fine. Have 5-6 traveling sales people with laptops. Looking for suggestions on how to get these people connected to the internet while they are on the road each day. Looking for something other than each people having an ISP account. They travel through out the USA and need access from different states. Have tried some of the “free” isp – looking for a better solution. Manily need to use email – send files to our main office.
Thanks