I'm not sure about Androids, but iPhones do not have a barometric pressure sensor, so the only way to obtain altitude data would be through GPS. For applicatio

I'm not sure about Androids, but iPhones do not have a barometric pressure sensor, so the only way to obtain altitude data would be through GPS. For applications like this, where you don't need real-time altitude information, that low-power GPS paper from Microsoft could come in handy, but it's cheaper and lower power to just use a pressure transducer in the first place.