You need a router that will connect to two different internet connections and load balance between the two connections. It will also provide failover but it won't be totally seamless since it requires a timeout to detect the dead connection.

I highly recommend the Linksys RV082 router. I used it at a previous startup and it worked really well for us.
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You need a router that will connect to two different internet connections and load balance between the two connections. It will also provide failover but it won't be totally seamless since it requires a timeout to detect the dead connection.

I highly recommend the Linksys RV082 router. I used it at a previous startup and it worked really well for us.

You can see more details at: http://www.linksys.com/servlet...

Multi-Homing Broadband Routers
The most direct method for utilizing two high-speed Internet connections on a home network is to install a router specifically designed for this purpose.
Multi-homing routers feature two or more WAN interfaces for Internet links. They handle both the fail-over and load balancing aspects of connection sharing automatically.
...

Multi-Homing Broadband Routers
The most direct method for utilizing two high-speed Internet connections on a home network is to install a router specifically designed for this purpose.
Multi-homing routers feature two or more WAN interfaces for Internet links. They handle both the fail-over and load balancing aspects of connection sharing automatically.

However, these high-end products are designed for use by businesses rather than homeowners and therefore can be complicated to set up. Due to the inherent overhead involved in managing such connections, these products may not perform as well as hoped. They are also significantly more expensive than mainstream home network routers.
Broadband Multi-Homing Without a Router
Those with technical know-how may be inclined to build their own high-speed multi-homing system at home without purchasing a router. This approach requires you to install two or more network adapters in a computer and develop software scripts that manage the details of network routing and configuration. Utilizing a technique called NIC bonding allows you to aggregate the bandwidth of simultaneous Internet connections.
Partial Multi-Homing Solutions
Network operating systems like Mac OS X and Windows XP contain limited multi-homing support. These provide some basic Internet sharing capability without requiring expensive hardware or deep technical understanding.

With Mac OS X, for example, you can configure multiple Internet connections and have the operating system automatically fail over from one to the next if a failure occurs in one interface or the other. However, this option does not support any load balancing or attempt to aggregate network bandwidth between the Internet connections.

Microsoft Windows also allows you to configure a similar level of multi-homing on a home network. Older versions of Windows required you to install two or more network adapters on the computer in order to take advantage of multi-homing, but Windows XP and newer versions allow you to set up the support using the default adapter alone.

Finally, installing two broadband network routers each with their own Internet subscription allows you to utilize both connections simultaneously, but only on different computers. Ordinary home network routers do not provide any mechanism to coordinate network bandwidth sharing between them.
Source: about.com
Hope this helps.