Taking advantage of large PC/MAC keyboard to type your SMS into a text file, then drag it into iTunes. A new SMS dialog will pop up on iPhone with the content of the file. Choose your destination phone number then press Send on iPhone. You have to press Send manually on iPhone for a security restriction by iPhone.
Work with your iPhone connected to your PC/MAC via USB cable, iTunes running on computer and with this application running on iPhone. No need of tethering. The data is exchanged between your computer and your iPhone via the USB cable, therefore the iPhone must be connected to the computer with the USB before you can see the SMS file sharing appear in your iTunes and before you can drag files into the SMS file sharing window as shown in Screen shot.
Useful when you have a long SMS or several SMS to type in a row. Suggestion: when you have several SMS to type, keep the same text file open in text editor , erase the old content, write new content, Save, or Save As a file on Desktop for the first time, and drag it from Desktop to iTunes for sending, go to iPhone and actually send it. Then re-write in the save file for the next SMS, Save, and drag it again into iTunes for the second SMS, etc.
PC: use notepad to write the text file.
MAC: use TextEdit to write the text file.
SUPPORT: firstname.lastname@example.org (phone model, os version,problem description please).