No. Unless you are an Autonomous System with your own address range, you cannot aggregate two lines to double the speed of a single host with a single address.
However, you can have two addresses with two separate lines (that will happen by default). The two interfaces will be exposed as different hosts, so (for instance) each tcp connection will have to use either one or the other. But depending on your operating system, you may be able to set up some rules to make some connections go trough adsl and others trough 3g. You can typically control this by changing the "bind address" of programs that use networking. The way to do it is program-specific.
It is probably more trouble than it is worth, however.
Another possibility, if you control some server outside on a fast connection, would be to put yourself on a VPN, make two separate connections to the vpn hub, and load-balance the routes between the two. Again this is not for the faint of the heart.