You will have to call Verizon and ask them to release your Blackberry Pin and IMEI or else you wont be able to have email service with the other carriers BIS Account. It was a pain for me when I had to travel to South America plus the carrier did not have my Blackberry in their system. I ended up just going with verizon roaming and had a cheap gsm nokia phone for my local calls.
Also keep in mind 3G may not be available in India.
cheap SIM are easy to find, HOWEVER not with BB data, those are tougher to find and more expensive. How vital is your email? You can just get a phone call SIM and then use wifi for web browsing and IM you should be ok using most 3rd party apps, Bolt Browser, Opera Mini, etc.