On my opinion you need to consider QoS deployment on 2600, like LLQ (make sure your ISO support it). Create traffic classes, ie voice class, data class, internet class,
etc. After that assign voice class into priority queue and very carefully assign bandwidth to it because any traffic that exceed bandwidth in Priority queue will be dropped.
Next question is how yo are identifying VoIP/VoFR traffic. I presume you have FR Network and your QoS done via map FR statements. ALso you need "LLQ for FR' feature on 2600.
Why not to classify voice traffic in the following way:
create Access-list for voice
# ip access-list extended neaxvoice
# permit ip allow IP traffic from PABX IP Address
class-map voice
match access-group neaxvoice
policy-map general
class voice
priority x set b/w
This should help.
Regards,
Vakhtang