Nikah on phone

Sir i have a question... what is the process of nikah on call?? my friend did aijab o qubool on a call just for fun at that time no one was on her side listening to her... but now she is saying that she was standing near the main door so it is possible thaf someone listened her from outside so i wanted to ask that in this condition is she married to that guy now? and tell me that what are the conditions for nikah on call... is it necessary to listen the aijab o qubool by witnesses by both sides on speaker??? or if witnesses hear only one sided talk from each side.... will nikah be done???