Not at all , and as i told you pass me your network topology and i can suggest you some recommendations.
You need at least one voice enabled gateway (Router) with interfaces that vary depending on your telephony requirements (FXS, FXO, PRI,.......)
Also , you need to implement Quality of Service QoS policy in conjunction with th ISP to deliver voice over IP for remote sites.
If you have in India an International Gateway that enables ISD calls over VoIP , it will be easier , the issue will be just to deliver VoIP calls from your campus to their campus through ISP WAN cloud but with QoS in order to maintain delay , jitter , packet loss within the recommended ranges in order to have a good voice quality
I hope this answers your request