There have been many first's from Airtel, but these days MTNL has launched quite a few new services.
The newest is the Voice SMS. It was launched on 21st February,2007.
How to use it??
I. Composing a message:
1. Mobile to Mobile & Landline to Mobile:
Dial 1* followed by recipient number.
2. Landline to Landline
Dial 1* followed by recipient number
3. Mobile to Landline
Dial 1* followed by recipient phone number along with STD Code i.e.011
II Retrieve new messages (For Landline & Mobile)
Dial 1*0* to listen to all new messages.
III. Retrieve old messages (for Landline & Mobile):
Dial 1*1* to listen to all old messages.
Note:This service is free for 2 weeks only, after that it becomes chargeable so better use it now...