WE ARE NOWADAYS privileged (if not spoiled) to make communication with one another through numerous ways and means. Long gone are the days where you can only be in touch with your far-away family members by posted letter or at a later stage by the conventional so-called landline telephone. At the very least, we are now able to reach anyone almost anywhere at anytime thanks to the mobile phone, or simply text short messages using the same device unless conversation is necessary, send a free e-mail in just seconds, or make long-distance photocopying (fax). We can even talk for free on the Internet using the likes of Skype or MSN Messenger in our spare time.
Some people, though, have a "home-made" insistence that if you try to reach someone by mobile phone but failed for any reason, the person contacted should return their call by phone too. If you send a text to someone, they should reply by SMS too. So their view is that it is not appropriate for you to send an email in response to a missed call that you received from someone. While I do respect this principle, let me take you to reality where this is not always practical and eventually inappropriate to being dubbed 'discourteous'.
Let's say this morning you've got a casual email from your brother overseas telling you that he's planning to get married this year. You're surprised and have so many things to question him about this plan. But you're quite busy at work that you have little time to reply to him by email, so you decide to ring him at home tonight instead. Is there anything wrong with this (email returned by phone)?
On another fine day, you heard a beeping tone on your mobile and opened the message from an old school friend saying that she's got your mobile number from another friend and she gave you her office email address as well in the message. You found yourself hilarious to find her again, and decided to just email her in response to the SMS thinking you'd be unrestricted to just 160-character (max.limit of 1 phone message) in expressing your joy and sharing all your recent updates with her plus asking for more detailed news surrounding her. In doing this, you've also let her know that you received her text message. Is there anything wrong with this (SMS returned by email)?
On one Saturday afternoon, you had a missed phone call from a work colleague. But you happened to learn of the missed call only in the evening around
Just from these three daily situations, any sane person should be able to conclude that there's really nothing wrong with a different way of responding to someone's trying to communicate with us. Which all come back to one's personal or specific circumstances and levels of urgency/importance of the message of the sender. The most important thing is that we make sure we do RESPOND to the person back, and so communication transpires in both ways.
The unacceptable thing (and hence discourteous) is when and if the person you emailed, SMS, or phone never reply your message (which clearly requires their response) as if you had never said anything to them before. They simply ignored you pretending they didn't know the answer or even worse they disagree on what you said/wrote but somehow are too timid to show you their differing opinion and therefore just staying silent to the end of the world.