Cisco 2811 SIP trunking to Asterisk?

I am in the process of getting Qwest Integrated Access service installed. It is basically a T1 that they split between voice and internet. The device that they use to split it is a Cisco 2811 router that provides me with a couple ethernet connections and one T1 connection. I currently don’t have a T1 card in my box as I have been using SIP trunking and would rather not spend the money needed for a quality one if I don’t need to. My question is this:

Can the 2811 support SIP trunking and would it possible to connect my Asterisk box to the Cisco 2811 router using this? I am free to make any configuration changes to the router.

From what I have read it looks like this may be possible, but I have not seen this done or spoken with anyone who has.