In the CTX admin software, go to Advanced Configuration>Station>Multiple Call Group. Create a multiple call group(say 650) and in the member tab, enter all the stations you want to ring on incoming calls and set them for immediate. Then put the voicemail pilot number in there and set for delay1 or 2. The timers are set in the previous screen. Then go to Advanced Configuration>Trunk>Assignments and in the DIT tab, put Dialing Digits as the destination type, and the multiple call group number in for the destination digits. So thats program 517 and 518 for the MCG, and 310 for the trunks.