Do you have a smartphone? If so, how do you address this?
Hope is the denial of reality. It is the carrot dangled before the draft horse to keep him plodding along in a vain attempt to reach it. We should remove the carrot and walk forward with our eyes open. -- Raistlin Majere
Unlike cellphones of the 90s and early turn-of-the-century, a smart phone is more than the sum of its parts... that is to say, it's all about the software. Before you even look at manufacturers, you need to decide on a mobile operating system.
Your main choices are Apple iOS and Google Android. There is, of course, also Windows Mobile but the largest share of the market belong to those two mobile OS systems. If you so chose iOS, then you're looking at an iPhone, if you choose Android you have some choices... the main competitors are Samsung, Google Nexus, HTC, Motorola, LG, or Sony.
I have never heard of Medion but I probably wouldn't consider it. Without mainstream support, then you are going to find very little in terms of accessories and applications.