Hello all, 

I need your help. I have made vpn in windows server 2008. All client can connect to the VPN, and the status of the vpn is internet access

At the company where I work, 80% of our employees are field workers. and all the field workers are required to use a vpn connection. The device they use to connect to the vpn is a GSM USB MODEM or ANDROID. My problem is, when our employees do not have a data package on the SIM card, they can not connect to vpn.

I've been trying to configure vpn server, but if my local internet connection is lost, the VPN participate disconnected, and when I tried browsing, FUP from my ISP joined truncated. Some articles I've learned, some say this can occur with a callback method. But I still have not understood what is callbacks and how to configure it. They say this can occur with cisco devices. But I do not know what kind of device is needed?

The core of my problem is how to connect to the VPN even without a data plan? or how to stay connected VPN, when a local ISP connection is disconnected?

Now I want to ask you.
1. Can my employees connected to the vpn even without a data plan, or when data is turned off?
2. If this can happen, what tools should I use? whether with enhancements such as a Cisco router or ewon?


Please help and thanks before ..