Detailed example of Fax
Person X wants to send a fax to Person Y; she knows Y's E.164 number.
Person Y has many IP applications tied to her own (Y's) E.164 number.
Device C became responsible for delivering the fax. Device C is Internet Aware, is ENUM-enhanced, can do SMTP and SIP, but can't do H.323 yet.
Device C does a DNS query on the E.164 number. Device C discovers from the response that Person Y prefers real-time to store-and-forward fax delivery, likes SIP and H.323 equally, and has SMTP, too.
Device C tries SIP first. If SIP fails, Device C does not try H.323. Instead, Device C then tries SMTP.
Note: Device C uses ENUM in its application selection logic. ENUM is an enabler and not the same sort of thing as SMTP, SIP, H.323, voice/fax/data, etc.