Almost all Telecom Companies has given the facility of balance transfer... just follow these instructions to transfer balance from one sim to another
Docomo
Send sms: BT(space)number in which you want to transfer(space)amount and sent to 54321
eg. BT 9000000000 50 and sent to 54321
(Join buddy net)
Airtel
Dial *141# and follow the instructions
Aircel
Dial *122*666# and follow the instructions
Rs.1 service charges for every transfer
you can maximum transfer one time in 24 hours
BSNL
Type: GIFT(space)number in which you want to transfer(space)amount and sent to 53733
eg. BT 9000000000 50 and sent to 53733
Vodafone
Dial *131*amount*number in which you want to transfer#
eg. *131*50*9000000000#
Charges will be rs. 2 to 4 for this service
Idea
Send sms: GIVE(space)number in which you want to transfer(space)amount and sent to 55567
eg. GIVE 90000000000 50 and sent to 55567