A telephone call is spontaneous: there is no advance notice of a call coming through. The most you can do is forewarn the servants (who act as a buffer) and hope they don't forget. An exception could be when you write to say that you will phone at a particular time. Thomas Hardy wrote to Lady St Helier in 1917, proposing "to ring you up on the telephone Wednesday morning to ask when we can call." Imagine the chaos today if we wrote to everyone first, announcing our intention to telephone them at a set time!
The visiting card represents its owner, the visitor. (Remember, you can't leave a card on behalf of another person who is out of town.) What represents the 'caller' when he telephones? In this respect, he is an unannounced visitor who contravenes social rules. Note also the slippage in meaning of the word 'caller': he is no longer a tangible presence in the house who sits opposite the hostess, but a disembodied voice heard coming from a handset. Implications for perceptions of the time-space relationship?
The rules for visiting are formal. Those who adhere to them are seen as upstanding members of polite society. What does it say about a person who bypasses these rules, engaging in innovations and uses a telephone?
The telephone's initial role was one of a business tool. Even when found in homes of the well-to-do, it was for the purpose of the householder/factory owner/businessman in communicating with his place of business. In this context, can we assume that the telephone has no place in polite society when ladies called on each other? Gentlemen rarely made such social visits, i.e. making morning calls.
A telephone call is (or at least, could be):
From a hostess's viewpoints, these are vulgar traits for a visitor.