I am going to release the new version of Zeroshell that also supports the USB modem Huawei E220 for 3G mobile connections. It includes load balancing and failover management of WAN link such as ADSL, cable modem and HSDPA/UMTS/GPRS connections. In addition, you can create LAN 2 LAN VPN in aggregation mode in which if you have more 3G connections you can increase the bandwidth of the layer 2 (Ethernet Datagrams).
Regards
Fulvio