There is provided a method for establishing a communication session between a client device of a caller and a client device of a callee, comprising: iteratively attempting to establish a communication session, via a communication interface of a client device of a caller, to a communication address of a client device of one of a plurality of callees represented as contact members stored in an electronic address-book, wherein each respective iterative attempt includes; detecting failure of the establishment of the communication session; applying a set-of-rules associated with the respective contact member and stored in a set-of-rules repository, to attempt to establish a subsequent communication session via the communication interface; and attempting to establishing further communication sessions defined by a sequence of the set-of-rules when previous attempts at establishing communication sessions have failed; wherein each respective communication session allows human language based communication between the caller and the callee.