1) Never delete your voice mail. The ability to check your voice mail on speakerphone when someone else is in the room and have them hear "You have 99 messages" is extremely useful.

2) Attribute the highest level of importance to everything you must do during the day. The mate you are meeting for a beer at lunchtime is an important meeting. This is why it is so hard for your clients to get hold of you and realise that you havn't touched their website for weeks.

3) Check your cellphone regularly for messages and missed calls. Push some buttons now and then. During meetings have someone (perhaps an autodialer on your computer) phone you. Look to see who is calling, then divert the call to your voicemail (building on #1). Do this several times, then answer an 'important' one, and excuse yourself.

4) Carry the bigest diary you can. Check it regularly in the presence of others. Just make sure they don't see that the pages are blank, or covered with crude pornographic drawings.
I can't remember where I read these, but they stuck in the back of my mind for ages. I actually started doing #2, and have used #3 to get out of boring meetings that can be re-scheduled. I'm sure you can think of many more ways. I personally like:

5) File everything in your filing cabinet. Flicking throuh thousands of little folders (really filled with a mess of sad jokes and guitar TAB) when you get your client's file out just has to leave an impression.