Interviewing someone over the phone is never easy, and it is a task that has been made a bit more difficult since the switch to mobile phones. Where as with a landline you could use something like the previously reviewed Mini Phone Recorder, there are no simple bypasses for cellphones.
I was originally hopeful when a previous reviewer devised a way to record cell phone interviews while wearing a hands free headset using parts found at Radioshack. But I wanted something simpler.
With a little bit of research I discovered the Olympus TP-7; a miniature microphone that slips into your ear and plugs into your recording device (or computer) and enables easy recording of phone calls. At $11 it seemed like a low risk move to try one out.
Given its low cost, I didn't have any expectations in terms of audio quality, but was surprised to find that it was crystal clear (or as clear as a cell phone conversation normally is, clipping and all). While it's true my questions were louder than their answers the difference didn't hamper playback and transcription. Furthermore, the TP-7 is comfortable enough in-ear that I practically forgot it was there (just remember if you ever switch your phone to the other ear you have to move the microphone as well). The TP-7 comes with a bevy of plug adaptors, as well as different sized ear plugs for a comfortable fit.
I have, in the past, tried Google Voice's recording services that only work on incoming calls to your Google Voice activated line (and also announce that the telephone call is being recorded due to varying state requirements). The recording quality is significantly worse compared to what my Olympus TP-7 and Olympus LS-10 produced, and the transcription (another feature offered by Google Voice) was laughable.
Also, unlike the previously reviewed hands-free setup, the TP-7 has the added advantage of being a single piece of equipment that requires no extra cables or accessories, and is small enough to be carried around in my bag all day just in case I have to record a call on the road. If you ever have a need to record phone calls or interviews over the phone (mind you, legally) I can wholeheartedly recommend this tiny, lightweight but high quality in-ear microphone.
-- Oliver Hulland