Question about Remote Access…

If i have a company located in Wisconsin, and this company has their staff or tour guides using notebook computers for logging tour details so they can communicate with their home office network.But each tour guide is required a secure method for connecting back to the home office network. Each of the tour guides has mobile broadband Internet cards. However, they are often in areas without access to cellular networks and have access only to telephone lines. What i’m trying to figure out exactly is based on the operation, what can i recommend to the company a way to implement and to meet the needs of their remote users???