Even though this change is made in a Contacts menu, your iPhone or iPad will remember which account is the default for sending emails. Go ahead and write your message in the Message field. Upgrade IOS on your iPhone to version 5 if you have not already done so. Likewise, the trigger shortcut should be something around letters for the most part and easy to remember. You can place signatures on text messages in a variety of ways, either through your phone or a third-party application. In Handcent, for example, go to "Menu," choose "Settings," select "Send message settings," check "Enable signature" and choose "Personal signature.