What is the expected load time for a website or email on a smart phone?

I saw couple of statistics showing page abandonment as loading time increases, but haven't found any resource which would specifically deal with "mobile" users only.

Obviously this question can be tricky since the download speed will depend a lot on the actual connection (2G, 3G, 4G) of the visitor, but still it would be exciting to know their behaviors.

Do you know about any study in this field?