if I have an 2821 with e1-pri and 8 analogs fxo's trunks. What is the pros and cons between those type of gateways if I have CUCM version 6.
For PSTN trunks you would always use either MGCP or H323. SCCP is typically used for analog FXS ports (fax, analog phone etc). MGCP is simpler to configure, but u lose control of the call at the gateway level. Every thing is controlled by Callmanager. In that way, h323 is more flexible, as you can manipulate digits at the gateway level. But H323 can be a administrative nightmare depending how complex your dial plan and your Voice infrastructure is.
WHile troubleshooting, H323 gateway debugs are easier to troubleshoot. MGCP debugs are "piece of ****"...wish the programmer did give some more thought into making it more user friendly...