so i did a bit research around the 3g version of the miix and found out that Lenovo already sold it in Singapore since the beginning of February 2014. But, and now i understand why there in the rest of the world is no 3g version because the internal modem or the antenna attached to it caused some trouble there. Most people had problems to get connection or hold the connection continously. So most of the devices which are sold there already get back for refund. So far is i read there should be there soon a 2. batch of the lenovo miix 2-8 with less problems at modem side.
I found out too that there was in the first batch a built in 3g modem from huawei.
here is a link with more informations from a special forum over there:
as far as i can see it should be possible to connect a modem inside this tiny tablet even it is not integrated at purchase. space is enough there as you can see on my pictures i took at the disassembling post. I will do some testings and will see what happens. this is the biggest lack of the miix right now.