Hello,
As Ben stated in this post:
We do not currently have many “Officially Supported” models, but if a phone has a strong enough GPU it will probably work for that as well. If you compare the Adreno 330 (The Nexus 5 GPU) to the PowerVR SGX530 (Droid 2) you will see that the PowerVR has a much weaker GPU.
There are plans to expand support as has stated. The best way to have that expedited would be to vote up this post:
That will let our developers know what the community wants more focus put toward.
Is 4.2 going to support all Android phones?
In 4.2 we plan on implementing a lot of updates, fixed and additions, but if you look at the trello board you will see that Android support is not planned to be expanded a lot in the immediate future. When we start expanding officially supported mobile devices, it will probably be in waves and not all at once also.
We do have a team of people working on it, but there are a lot of hardware limitations that we have to build around to make UE4 work for those older models. This is really important to us, so you will probably see more announcements about Android support in the coming months.
I hope that helps to clarify.