I don't think it's just the PM's but more (for me anyway) not being able to post pictures, vids and editing post. (My typing is atrocious, especially when I'm on the tiny mac keyboard.)
Basically from what I can see, without the premium membership you will be able to post a topic and reply to a topic.
Cinds you can still edit a post for a set amount of time ... after timed out then no you cant ... u tubes can still be posted - it is personnal vids etc and pictures from your PC that you have to pay for
see quote below from edited OP
Edited by El Loro - The Upload Videos etc refers to videos etc you have on your computer and want to upload on to the forum via an attachment. Youtube clips etc and photos from other websites can still be included in your postings here without being a VIP.
If you want to edit a posting you still can provided it's within the grace period (I think that's an hour or so). After the grace period has ended you cannot edit a posting without being a VIP.
I am assuming photo bucket etc counts as another website