In case you don't know, only one non-governmental organisation has EVER put something in orbit. SpaceX. Cost $100Million.
There is a competition in full swing at the moment called the N-Prize for orbital attempts. but no-one has won that yet. Or even got close.
John Carmack of Doom/Quake/Rage fame runs Armadillo aerospace and has a lot of rocket experience. His last effort to just get to 100kft crashed and burned. (STIG)
Copenhagan Sub orbitals are trying to get to orbit - they had a low altitude test earlier this year which sort of failed. At least it left the pad.
All the above use customised electronics. I think a mobile may not be robust enough for what you are planning. A raspi might work, and would be easier than modifying a phone. As someone else said, the electronics are by far the easy easy easy easy bit. If you think they are hard, then you might have trouble grasping how difficult getting stuff up there is. It's not that rocket science is difficuly, it's that rocket engineering is VERY VERY VERY difficult.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
“I own the world’s worst thesaurus. Not only is it awful, it’s awful."