I am notorious for writing down names, numbers, notes, what-have-you on random pieces of paper and then losing them. Luckily, a few years ago, I came up with a plan that changed all of that. It's my favorite organizer...A simple whiteboard on the fridge.
When I'm the phone and need to write a message, the whiteboard is right at my fingertips. I just jot down the message. Best yet, since it's right there at eye-level every time I open the fridge, I never forget the message either!
Need to leave an important phone number for a sitter? No problem. Use the whiteboard.
Over time, I also started using certain areas of the whiteboard for recurrent needs like a grocery list, the meal menu for the week, a honey-do list for my husband, etc. Your whiteboard will become as unique as useful as you are.
And, here's the best part. It's cheap. I bought a simple whiteboard from Walmart for a few bucks and then glued extra magnets on the back with superglue (the cheap advertising ones I seemed to have all over my fridge). I highly recommend the dry erase markers they have there too since they are magnetic and have erasers. I just stick them on the fridge and always have them handy when I need them.
Good luck and happy remembering messages.