Im going to move to Africa and needs fast connection. Several providers have 3g. I wondered if I could buy 2 or 3 3G dongles to get the speed up? Is it possible to set this up in any software or router?
You could, but it will not be as straightforward as it seems. Each USB dongles creates its own network, and it will have its own external IP address. You would then need to route calls to one interface or to the other, according to some rules, which you would need to create.
For simple cases, it could be OK: you could route everything that goes to your company via dongle 1, and all public internet through dongle 2. This can be done at operating system level without further requirements.
However, if you want to achieve load balancing, it will require some dedicated component which would route traffic through one dongle to the other. It would need to be smart enough to keep each "session" on the same dongle, because visiting a site from two different IPs, especially if you are logged in, will not work.
I found this: http://www.peplink.com/max-mobile-router/compare/ which may help you as a starting point.
Also this is an interesting project: http://arstechnica.com/information-technology/2013/10/new-router-combines-your-home-and-mobile-networks-into-one-faster-pipe/
I have managed to successfully do this using two 3g broadband routers and 2 3g broadband dongles. 1. setup both routers to use the 3G dongles as normal. 2. On one router setup the wireless for bridging. This extends your wireless connect throughout your home but as a consequence it doubled my broadband speed from 1.5MB to 3Mb. Only problem with this is its using twice as much of my metered data connection.