Asteriks Voice Mail server threw SIP

Hi everyone been a while since working with asterisk and not familiar with sip. Here is what I am trying to do. Use asterisk as voicemail server for small cellular system. I can handle the dial plan and the mailbox is pretty sraight forward but cant figure out the sip trunking part between the cell switch and asterisk. Any help on sip trunking would be greatly appreciated :smiley:

Update figure out after talking with switch engineer that it will be a lot easier for me to use T1 instead of sip.