I belong to another forum that you can't directly from iPad, iPhone, or android phones, if you have all the different options on. It is older forum software and it would need to be updated in order to work.
A couple of work arounds we have done have been to either, pick in our user option, to have basic messages (which will mean no smilies or formating). But then when you are back on a computer you either have to change it back or not have all of that. The other is that we click on the html button and type our text in that area. it also means if you know the html code for any formating you want (ie bold or a smilie) you can put it in there.
It seems to be more of an out of date forum server issue than an iOS or android issue.