I have Nortel Meridian One Option 11c in Head quarters. In remote site, phones communicate to PBX through a T1 connectivity between remote site and HQ.
I want to migrate to VoIP. Can I simply use the T1 as a data T1 and connect it to csu/dsu interface card at both HQ and remote site and send IP without any changes in Telco who provides this T1?
Yes, with two voice-equipped ISR routers you can do that.
Recommend you located a reputable/voice certified cisco partner for the jor, or you risk being taken for a long and expensive ride.