SIP VoIP phone --> asterisk

I have a SIP Linksys phone which can be connected to 2 SIP servers…1 is a server of a VoIP telco that I have it connected to and another could be my asterisk box…

Is there any way that I can route calls that come to this phone form any PSTN number through the VoIP telco so that i can execute an Asterisk dialplan on them???