Long Distance WAN Solutions?

Kreiger asks: "A client of the 'Big Five' consulting firm I work for is looking to implement a mid to large-scale WAN, the only issue is that some of the sites that they want to extend the WAN to are incredibly remote (some of these places can only be reliably reached via satellite phones). Does anyone know of any proven (or at least non-vaporware) WAN tools or vendors that can handle this sort of thing?"