This app is an easy to use workaround for situations where operator/ROM incompatibility prevents users from activating call waiting (ability to receive calls while in call) in Settings -> Call settings (-> GSM call settings) -> Additional settings.
Call Waiting Enabler requires the following permissions:
All these permissions are required to dial MMI codes (by which call waiting can be activated and deactivated).
Call Waiting Enabler won't enable call waiting in cases operator doesn't support it or has prohibited this feature.
This software dials *43# to activate call waiting, #43# to deactivate it and *#43# to query status. This app was created mainly because there was no such app in Market and finding these codes wasn't very straight forward (when searching for alternative solution to enable call waiting on Android phone).
More info on website.