Mobile phones used to be slabs of plastic that let you talk to people. New features and tools have turned once simple devices into pocket computers. Today’s smartphones are powerful computing devices, capable of running a wide selection of applications, with tweaking utilities as well as development tools and SDKs for writing your own code.
We’ve grown used to having general-purpose computers on our desks and being able to change everything about them - from adding new hardware to modifying operating system kernels to get better performance. We can’t do that with phones. The most hardware you can easily add is a memory card or a Bluetooth GPS. Often new applications have to be certified by operators, and even when there’s a new version of a phone operating system it can be a long wait before (or even if) it’s ready for you to install on your handset. Applications are constrained to work with tightly controlled APIs, with little chance of getting the most from phone hardware.
Hacking Your Smartphone | Tom’s Guide