As a feasibility study, the primary emphases of the trial are to demonstrate the investigators' ability to recruit and retain participants, to test whether their proposed enrollment criteria identify the appropriate patient population, to assess participants' levels of adherence to all aspects of the protocol, and to determine optimal methods for data collection. The investigators will compare two different smartphone-based applications for collecting headache-diary information and will test the logistics for employing interim Bayesian monitoring. No tests of clinical effectiveness will be performed.