You were doing it wrong. The "subject" box is actually split into two horizontally. Top portion is the subject (if text is entered here it becomes an mms), and the bottom half is the message itself.
So to send a regular SMS you would just enter contact and the lower section of the text box.
As has been mentioned already though, much simpler to turn off "subject" box (mine was by default). This means a message is sent as an mms only if you chose an attachment and actually select to send as mms.
Yes well it works now lol...i turned off the subject field so thats fixed it...although before doing that even if i didnt add the subject field it would still send as mms but trying it again ie turning subject field back on and not putting in the subject...it sends it as a normal sms....strange but probably something to do with the fact that my sms werent being sent even after turning off subject field...got it sorted out with tmobile, they sent me the settings for the service center.