Jerry wants to record webinars and wants to know if he can use an external microphone to do it. Leo says he could, but you'd need an adapter for the minijack on the phone. He recommends just using the microphone on the phone. It'll work fine for that. He could take the direct out of the computer using the PC's headphone jack, and then plug that into the jack on the phone. That should bypass it altogether. One other option is to get a directional mic that will plug into your phone as well. Or even a parabolic mic. RODE makes great models with minijack connectors.
Robert is an aspiring filmmaker and he uses a DSLR to make his films. He's planning to upgrade to a better platform, but wants to know how he can improve his audio. Leo suggests Beachtek. They make devices that will allow him to run real XLR microphones into his camera's minijack and take advantage of better preamps as well. That's the best place to start.
Marty has a DSLR camera and when she shoots video, she hates the quality of the audio. What can she do? Leo says that the on board microphone is terrible, but most DSLRs have an external microphone minijack that will allow her to add an external microphone. Rode has a great one called the Video Mic Pro. That's the simplest solution.