Are you sure? The limit is 160 characters.
Try using a different SMS app. If it persists, we have to know when t's happening. Does it do something when you type the 44th character? Or does it give you an error when you send the text?
Are you using English, or some language that uses more than 7 bits per character. (The actual limit is 140 octets, which works out to 160 7-bit characters.) If you're usng a unicode alphabet you're limited to 70 characters, since it uses 2 8-bit bytes per character.