Are you trying to record Midi or the sounds of your td4? You are not specific.
Remember, MIDI has no audio content, so connecting the midi out of the td4 to the iphone will only result in MIDI being recorded...sorry if you know this, but many dont, so I thought to mention it.
TD9+6v module, KD-8, custom Diamond Electronic 12" snare + 2x8" + 2x10" toms, PD-85, 4xPD8, 2xCY8, CY-5, CY-12r/c, Pearl P902 double pedals, Diamond Electronic COWBELL!
HPD-10 ATH-50M phones and 4 Vex Packs for the TD-9
Gibson Les Paul. + pod xtl, Norman acoustic, Fender J-Bass + gt10b
Clavia Nord Stage 2 Synth/Stage Piano Samson SR850 'phones
cubase, garritan personal orchestra, JABB, symphonic choirs, Sibelius, reason 6.5, IPAD 2 with lots of soft synths...
three shelter cats