I'm thinking about upgrading to a smartphone for the purpose of collecting data for training tracking purposes. Therefore, it would need to interface with speed, HR, and cadence sensors, so I would probably want Bluetooth (although I'm aware that some phones may have internal ANT+ or I could use an add-on ANT+ device). I would want it to be able to store downloaded GPS maps in memory so I'm not locked into needing a data plan to operate it. It would also need to be able to run suitable apps to make all that work. Finally, I would need it to work with wifi at home or free wifi where available.
I'm leaning heavily toward buying an older used smartphone, which I may or may not want to use as an actual phone for voice/text (more on that below). I'm open to either iphones or android phones.
My question is, what are the minimum/recommended specifications for a phone that will do all that reliably in terms of operating system, processor speed, memory, etc?
For more context, I'm pretty frugal and I don't really have the desire or need to operate a smartphone with a data plan at the monthly cost necessary to do so. I have an old flip phone on a Verizon pay-as-you-go plan that gives me far more minutes than I need at $15.99/month (although it sucks trying to text on a number pad). It would be nice to use this hypothetical smartphone for voice/text to avoid carrying two devices around, but I'm learning that there are substantial limitations to making that work (i.e. phones originally provided by one carrier, like Verizon, may not work on any other network).
My wife's work is offering a killer deal ($50/each) on an iphone 4 because they're about to upgrade to the iphone 5, but I've already determined that these Verizon iphones won't work with my existing plan, nor can I use one on Tracfone. However, it might be worth it to use it for bike use or the occasional game.