Deleting message code from other phone

The manuals for the AT&T 1738 can be viewed and downloaded here:

http://telephones.att.com/telephones_ui/support/dsp_manual.cfm?manualID=21714

Here is what the manual says about deleting messages remotely:

DELETE MESSAGE Press and release 3 while the message is playing.
DELETE ALL MESSAGES After you have listened to all messages and heard the
two beeps, press 33.