Nationwide mobile number portability has been launched in India, after a test launch in one region.
Idea Cellular – and lately Vodafone – have been advertising the service heavily on TV. On Jan 20, other providers took large ads in major newspapers alongside the government’s announcement, inviting customer to switch – to them.
Here is how you can go about it ( courtesy MoneyControl.com): To shift, send an SMS* from your phone to 1900. Your present company will reply with a unique porting code. Use that code while filling out a detailed form for the company you want to shift to. Within 48 hours, that company will take over all your cell services. The fees, about Rs 19.
Your cell number will be switched off for only one hour. All bills after that, are paid to your new company. You'll be stuck with them for at least 50 days before you can shift again, so choose with care.
While you can shift from a GSM service to CDMA or vice versa, you cannot shift from one state to another.

* sms format:PORT<your mobile number>     Send to 1900

Jan 20 2010