OTC is not the sending of cash in the mail or wire transfer.
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http://shadowlife.cc/2012/11/necessary-conditions-for-the-long-term-success-of-bitcoinWhile that is a lofty goal, until the density of local traders increases these methods help as an intermediate step. For instance, last month when the majority of cash deposit methods available in the U.S. (BitInstant, Bitcoins Direct, BitFloor, BitMe) went down at the same time (temporarily, fortunately) there were some people really in dire straights. These are people who are now using bitcoins as a substitute for cash. They've come to rely on the ability to visit a bank or 7-11 and convert cash into bitcoins.
Unless there already was an easy method that allowed them to use cash to acquire bitcoins, they would never have gotten to the point where they rely on there being a supply of bitcoins. If the only way to convert cash to bitcoins was to locate and transact with a local trader, most of these people would never have gotten started. But now that there is a demand for bitcoins this volume is now becoming sufficient to make it worth the effort for individuals to become local traders and begin offering to do OTC exchange.
The network had to build up before the network effect began to yield much value.
But we're seeing that now.
Look at the growth of offers to trade through Local Bitcoins for instance.
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http://www.LocalBitcoins.com