Texts changing to a multimedia msg

I like to text my friend in England and as I do write more to her then an ordinary text it gets changed to a multimedia msg as it exceeds the limit, but when i try to send it, it says unable to send, and in your manual of the motoKRZR k1 GSM, it says that if it changes to a multimedia, I just press the yes key to send the message so it should go through. I have rang my phone server people and they couldn't help me, just said you will have to do lots of small texts to send. But I think that is crasy, when it does allow me to send multimedia in your manuel, but not work when I try it on the mobile, on my phone under the Message Setup it says Multimedia Msg Setup, and under that it says Text Msg Setup, then Folder View, and then Auto clean up, then Alert, then signature. So as it has all of these how do you set up Multimedia to work, so that I don't have to keep on sending her very small texts, and for me to be able to send her just one bigger one, without it keep on telling me it has changed to multimedia, but is unable to send my message. If it has this feature, please help me to access it, I really don't have much time to sit at the computer to type her messages, but I do love to keep in touch by mobile to her, and am upset that I can't get my messages to her because I have hit this brick wall of it not going through to her phone, ( by the way her number is correct, my old phone, which is broken, thats why my husband brought me this great motorola, worked great, and I had no problem of it not going through, I hope you will be able to help me, and tell me how to make the message go through to her in the multimedia Msg message. I appreciate your help in this matter, thanking you very much, from Tina SA.