I actually used a small spiral notebook for mine. I wrote down the times and what I ate or drank, when I went to sleep, when I woke up, when I engaged in specific activities and for how long, as well as when a migraine would start and rated it for severity, then made a note whenever the pain changed. I learned that any drink that was too cold made it worse, hot tea made it better, white cheeses were a trigger, artificial sweeteners would lay me low for days, etc., etc. By the time I went to my doctor, I already had a list of triggers and things that helped, and he went through to find a few I'd missed. like interrupted sleep was worse for me than no sleep and all dairy was bad while I had a migraine. He also suggested I not fold my laundry straight out of the dryer, and bring the laundry upstairs to sit on the couch while I folded it. Less bending equalled less pain so quickly I couldn't believe I'd missed that one.
Your doctor can give you a tracker that the drug company provides his office, but it's not really as good as making your own. If you want to use your cell phone to track your headaches, try using a facebook or twitter account you don't make public. Go all-out, the way some folks do the twitter thing, anyway, making notes of every inconsequential moment of your day. However you track your headaches, the more information you have, the better your doctor can identify your triggers.