Presume the Vigor 2860 load balancing router, the sales stuff talks of load balancing but nothing to confirm it will work across the ADSL and a 3G/4G device. Certainly across two ADSL lines is possible.
Might be better to go for something like Quad WAN load balancer
and then just concentrate on getting the various methods available as Ethernet e.g. use something like this Huawei router
to host the SIM card.
Another option is something like the Asus RT-N66U which others a load balance or fail-over mode from the Ethernet WAN with the USB 3g/4G interface (i.e. just get a compatible USB dongle). The Asus router with same mode (I believe) and a built in ADSL modem is the DSL-N66U