ECS (Electronic Clearing Service) or direct deposit in bank account is become a popular way of getting refunds these days. They are fast, cheap and easy to process. From Jan 2006 SEBI permitted use of ECS for IPO refunds. They started with 15 big cities and slowly moving to other cities. Below are few facts about ECS:
It's not mandatory for IPO Registrar to send refund amount through ECS.
It's up to a registrar to choose city in which they want to send money through ECS and send remaining refunds through registered post.
Even if registrar issued ECS in your city, it's possible that the bank information you provided is not correct and you may not get refund through ECS. In case of wrong or incomplete bank account information, registrar sends the refund through cheques.
For ECS, your bank account should be in the city where registrar is issuing refund through ECS.