This question is about low end mobile phones which cost around $50 to $100, unlike Smart Phones like iPhone or the ones that support Android.
Nokia 1280, 1800 are some examples.
I want to customize the basic features such as Contacts, SMS in such a phone. So I either want a open source code of its firmware that is compatible with one or more of such phones, or I would like to know of a vendor who could sell a cell phone within this cost range along with the source code of the firmware?
Do these phones have any OS running in them? Or just a single threaded firmware program?