dual ISP / fault tolerance

Here is the problem:

We have two ISPs – one provides a T1 and the other is a backup DSL. We have a sonicwall firewall that takes two different ISPs and provides outbound fault tolerance. If the T1 goes down, we can browse the web over DSL. However, customers and remote offices can’t see our website or send us email. Does anyone know of a device that will provide both outbound AND inbound fault tolerance for 2 different ISPs?