Best plan for making std calls from TamilNadu

[netsaint]

Hi all,I’m currently using Airtel Corporate postpaid plan, which I got through my office. Now I have bought a new mobile for my parents at home. But I’m confused as to which plan should I use for the new handset (for use at home). My parents make lot of STD calls from tamilnadu to bangalore, mumbai & parts of Kerala. The number of local calls they make are relatively less.So can any one advice me as to what plan should I select for this requirement? I prefer postpaid plans as you don’t need to recharge them often.- I’m open for other mobile providers also. So please let me know if you think plans in Vodafone or BSNL offer better rates.Thanks in advance