Nearly all, if not every single mobile device, is catered to the right handed user. With between 70-95% of the population considered to be right handed, most mobile manufacturers design devices with this in mind. This leaves the remaining 5-30% of left handed people having to adapt to a right handed world. User experience is one of the most important aspects designers will consider when developing a new device.
For left handed users, there is light at the end of the tunnel! Android have a hidden feature that allows you to switch your layout from right to left handed.