I encourage people to develop open source applications for this and other functions. At first it was impossible to do so on iPhone/iPod Touch and not violate the Apple developer agreement, but they have since revised it.
If you jailbreak and use the open toolchain, you can do whatever you want. Celestial is slick for playing media files, but you have to use AudioQueue for sample-level audio synthesis (e.g. Morse, PSK31). Ugh.
Developer access (which you need to develop apps and run them on a real device) costs money, but it's pretty nominal, and Apple give basic support to anybody who asks nicely. Be advised that the SDK downloads are huge, and take a while even over fast connections.
Laura Halliday VE7LDH "Que les nuages soient notre Grid: CN89mg pied a terre..." ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
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