Three sizes of phones with various layouts will give several device style options, module configurations.
With its first developer conference on the horizon, Google has just released the first public version of the Module Developers Kit (MDK) for Project Ara. While things are still very early, the MDK gives us our first in-depth look at how Google is leading third parties into creating Project Ara devices and modules, and how everything will fit together.
The main point of the MDK at this stage is to make third-party manufacturers aware of the guidelines that will soon apply to them for making Project Ara pieces. From what's shown now, we know there will be three sizes of phones — Mini, Medium and Large — with Large being released at a later date. Each size will start with a basic "skeleton" that will then accept components to build a phone, primarily sourced from third parties. There will be different device layouts available within each size category, each giving you room for specific components.
Basic phone components such as Wifi modules, batteries, displays and speakers naturally have specific restrictions on their size and design as to make them all work together, and manufacturers will be required to follow them. Google even goes in-depth into how camera modules, for example, will be a specific size and use certain shapes. The early MDK includes reference designs and CAD files to get manufacturers started with basic modules as well.
Google is apparently targeting early 2015 for actual Project Ara devices and components to go on sale, with an online "Module Marketplace" for these third-party parts giving you options to configure your own device right from the start. While we're keeping in mind that this is a version 0.10 release of the MDK, the specifics shown here give us a lot of hope for the launch of Project Ara and truly modular phones.
Source: Project Ara