Yes it is. In the eyes of many people, MMS is 'SMS with pictures'. It is presented in the same way and in the same interface as SMS on almost every phone that supports MMS.
In terms of end result (instant short messaging) and interface, they are directly comparable. The huge technical differences are completely hidden from the user.

It would cost me a few pence (about twice as much as an SMS) to send an MMS, if they weren't covered in my calling plan. It costs me nothing to receive one.

I thought that the mainland Europe networks wree generally more advanced and supportive than the UK ones are, perhaps I was mistaken. Almost everyone I know has sent and/or received MMS