Does contacting by mobile phone equal seeking permission to enter homes, and are three calls sufficient? And must I return the call of whoever called me?

Shaykh Bakr Abu Zayd mentioned that calling on the phone is not considered like seeking permission to enter houses. Therefore, the ringing of a phone call is not limited to three rings, because the wisdom behind seeking permission – which is to guard against looking inside – is not applicable to phone calls. However, moderation is necessary, and one should avoid excessiveness and exaggeration in the number of rings, to prevent annoying the person being called and those around him. It is not necessary to call back someone who called you, unless it is at the request of someone whose obedience is obligatory, like one's mother, or if not returning the call would lead to a harm that can be averted by calling. Nonetheless, it is preferable to return the call, as it reflects noble character and avoids hurting feelings.