How to allow custom text message in "Send to phone"

Currently the "Message preview:" shows hardcoded message which cannot be edited.
How can I allow (if possible, number of words limited) to edit it ?

This is necessary as text in that box like "http://mysite.com/drupal/node/1" shows up in sms http:/%2Fmysite etc.

Also, after the sms is sent there is no status message so that the user is not sure what happened.