Asterisk transfer to Cisco Voicemail

I’m having an issue transferring callers to voicemail. Right now we use Asterisk 1.2 to handle voicemail and SIP trunks. The current setup is working fine but we are migrating from Asterisk Voicemail to Cisco Unity Connection. The Cisco Voicemail is setup on ext 5600 and works fine when the caller is on the Call Manger. If a caller dials in from a SIP trunk the internal phone on the Cisco Call Manger cannot transfer the caller to the Cisco Unity Connection. The setup was already in place and I only know a little bit about Asterisk. I’m sure it’s just a dialing rule but not sure what to add.