I have somewhat found out the UICC call lock in an xml file present in LGTeleService.apk in LG Volt. This file is found in system/priv-app. It indicates restricted second call. I have tested a modified one where this lock file is not present. The modified one is here in this link. The mod one seems to have GSM/CDMA capabilities but GSM not tested. Take a backup/remove original files from system/priv-app. The files are LGTeleService.apk and LGTeleService.odex.
http://www.4shared.com/mobile/n27b1AQBba/0B5JEnvV5rooXdEhNNXZ6S1FTUTA.html
Rename this linked file to LGTeleService.apk
Post your feedback after testing on Reliance and Tata Indicom. Data does not break after this and is not fatal to the filesystem of the device.