Airtel, Vodafone, Idea and Tata Docomo has emails to which you can send queries: 121@in.airtel.com for airtel, corpcare.kar@vodafone.com for Vodafone, customercare@idea.adityabirla.comfor Idea and  listen@tatadocomo.com for Tata Docomo. Let us see what are their response times. 

My query is: If I am doing cal forwarding while on roaming, is it chargeable as per roaming rates, or will it deduct from my free minutes?

Note that this is a real question anyway.

Updates

All mails were sent around 7.45 AM.

First impression

I got automatic acknowledgement from Vodafone, Idea and Tata Docomo, but not from Airtel.

First Reply - Tata Docomo

Tata Docomo replied back on 10:22 AM, stating that: charges will be chargeable as per roaming rates. 

Second Reply - IDEA

IDEA replied back on 1:44 PM that: Call divert service chargeable as per roaming call rates.

Will update further responses here.