The other day, when I was in a travel agent's office, I was fascinated to listen to her spelling my name on the phone: Delta, Romeo, Uniform, Echo, Tango, Tango. It's a clever way of helping to prevent confusions and misunderstandings, and a practice I normally associate with airline pilots.
A friend reminisces that it was used in the old days by telephone operators, too, when putting through calls on those old plug-in switchboards that involved a bewildering web of wires. (She's actually quite young, so please don't think she is pictured in the charming old scene above!)
However, I find from a recent thread of discussion on the Maritime History discussion list Marhst-L--which is sponsored and administered by the Marine Museum of the Great Lakes, with assistance from Queens University at Kingston, Ontario--that the phonetic alphabet is maritime in origin, and closely connected with flags.
A page on the Naval Historical Center website explains it all.
The practice began in the early 1900s, it seems, and has been adapted as the decades slipped by. Back in 1913, A was Able, then became Affirmative, which reduced to Affirm and finally became the much more gutsy sounding Alfa. Similarly, Boy for B evolved through Baker to Bravo, Dog for D to Delta (one wonders when it will change to Dubya!), and E for Easy to Echo, while Fox for F became the much more bouncy Foxtrot. In the same spirited vein Watch for W eventually became Whiskey. As for R, using Roger (which also means "understood") proved too confusing, and so became the sexy Romeo.