The absolute best option is to install a proper linux-based router.
I have a Mikrotik router, and routinely use 2 ISPs at the same time. Swapping between one ISP and another is a simple process of "click"

It is even possible to automagically change from one ISP to another based on some rules.
The big advantage here is decent routing - so all "local" traffic for example can go down your cheap-as-chips IS local only account, and international via a SAIX account. Ditto for gaming. Got a omg-that-cost-a-fortune unshaped 1GB account for WOW? No problem - only allow WOW traffic on that ISP account, and everything else on IS, for eg.
Adding connections for a WiFi account, iBURST account etc? No problem - same process. Add a VPN? Easy as can be.
The only thing that will not wort is Neotel - because of their stupid phone. But that is another story.