The solution to this problem is to setup a local Peer-To-Peer wireless network with Internet access in locations that have two or more employees and use a "Cloud solution" that will enable everyone to have access to shared data at anytime and from any location.  For those who travel give them a Wifi Hotspot, Aircard, a USB Modem or turn on the Hotspot feature on their phone.  Using their laptops or mobile devices, everyone will be able to connect to the Internet and access the resources in the Cloud when they travel.

Then setup a wireless local area network in the main office with a Wireless Access Point (WAP) or Wireless router that gives access to the Internet.  When employees arrive at the main office location they can access the local wireless network.

The "Cloud solution" is very inexpensive and comes with very good storage capacity.  With this solution you can avoid the cost of setting up a server based local network and establishing remote access to it.  Subscribing to a local Internet service will provide greater access speed than the MiFi (hot spot) or USB Air Card connection.