While the new generation of hand-held devices, e.g., smart phones, support a rich set of applications, growing complexity of the hardware and runtime environment makes the devices susceptible to accidental errors and malicious attacks. Despite these concerns, very few studies have looked into the dependability of mobile phones. This paper presents measurement-based failure characterization of mobile phones. The analysis starts with a high level failure characterization of mobile phones based on data from publicly available web forums, where users post information on their experiences in using hand-held devices. This initial analysis is then used to guide the development of a failure data logger for collecting failure-related information on SymbianOS-based smart phones. Failure data is collected from 25 phones (in Italy and USA) over the period of 14 months. Key findings indicate that: (i) the majority of kernel exceptions are due to memory access violation errors (56%) and heap management problems (18%), and (ii) on average users experience a failure (freeze or self shutdown) every 11 days. While the study provide valuable insight into the failure sensitivity of smart-phones, more data and further analysis are needed before generalizing the results.