The power of any dramatic monologue lies in the scale of the dramatic moment upon which it is focused and the charisma, or uniqueness, of its speaker. In Wole Soyinka's "Telephone Conversation," the drama of the poem centers upon the moment at which the speaker's potential landlady asks him, in reference to the color of his skin, "HOW DARK?"
"Telephone Conversation" was first published in 1963 when the civil rights movement in America was campaigning vociferously for equal rights for black citizens. This moment in the poem, when the landlady asks the speaker how dark his skin is, would have have been particularly resonant at this time. For a modern reader, living in slightly more enlightened times, this moment in the poem might be even more impactful. It seems preposterous and outrageous that a landlady should ever ask such a question of a potential tenant.
The speaker in the poem is unashamed, eloquent, and, also, witty. For example, he tells the landlady that she should see the "Palm of [his] hand" and the "soles of [his] feet." These, he says, sarcastically, are "peroxide blonde." He also says, in mock lament, that he has "Foolishly ... by sitting down ... turned [his] bottom raven black." These moments of caustic, mocking wit certainly qualify as charismatic. These moments also help us to understand just how ridiculous the landlady's question is.