When Redpark (http://www.redpark.com) first introduced its RS-232 cable interface in 2011 for the iPhone iPad and iPod tough, Arduino users needed to use and a adaptor (rs232–>TTL).
The new RedPark serial cable (US$59) includes a TTL (Transistor-Transiistor Logic) interface. With a built-in TTL interface the new cable makes it far simpler for Arduino and other users to use as it does not require yet another adaptor for use, according to the folks at Redpark.