The rings are set by using "RCO 0/1/2" each having a different value, this is set on the pabx, so there is no sure way to determine from here what each value is. You can get the value by printing the CFN from LD 22. Also ensure the CLS on the phone is set to FNA, SFA and FBA
LD 20
REQ: CHG
TYPE: xxx
ECHG: yes
FDN 7000
(Voicemail DN) CLS FNA SFA FBA
RCO 0
(or 1, or 2) Goodluck! 