Now think about the traditional telephony business. I have to dial, you may have to answer. Voicemail part-automates the answering, generating more metered minutes. But you have to ask yourself: is it really the best you can do? Is it impossible to broaden the business model — temporary buddies, address book access, directory, etc.? Can’t you deepen it too, and automate previously manual business transactions via APIs?

If I were a telco investor, one of my key criteria of comparing the various “voice nets” (PSTN, mobile, Skype, open SIP, etc.) would be the existence, quality, adoption and economics of the APIs.

UPDATE: You can bet that a lot more than 45% of eBay’s margins come from these transactions. And note how their business model has no upper bounds imposed by human action; an automated voicemail answer still requires a human-initiated phone call. Now, start to imagine your voicemail box (with a sensible UI) as your “RSS feed of the most important stuff” like customer service messages from your bank. Et voila! You have a platform business.

Martin keeps his mo here.