The ideal solution would be a certificate based VPN that advertised a static local network via a dynamic routing protocol over the VPN. From memory you can do this with a Cisco VPN but probably also possible using an SSL VPN. The VPN calls home so you don't need to use a direct APN, Static IP or DynDNS.
Not an easy solution to set up, but one that will scale if you think the number of sites will grow over time.
nathanbiz: I've found our experience with the Huawei B970b to be average. Anyone else?
Do you have it connected yet or still waiting?
Our Huawei B970b sometimes loses connectivity to the internet for a 1-2 minute period maybe 3 or 4 times per day. It seems to get worse the longer it has been running since the last reboot. During one of these brief outages, it doesn't say that it is disconnected, but all traffic ceases. Then it magically comes back again, all by itself. Very strange but I've learnt to live with it.
My Telecom MF636 data stick sometimes behaves in a similar manner. Maybe it is a characteristic of 3G cellular data services?