As soon as you buy a new one the old one will be found. hahaha.
But seriously, we found my son's cell phone (6 months later) deep in the crevices of the couch.
When the kids were preschoolers I came home from grocery shopping in the pouring rain. I dropped my keys on the mat right inside the door and then my husband and I proceeded to get the groceries in the house, unpack them, make dinner, etc. The next morning I could not find my keys - looked high and low. I ended up taking my husband's copy of my car key off his ring, had to make a copy of the house key, etc. Months went by - my husband kept saying "I don't understand how you just lost your keys - how could that happen..." He must have said that 50 times over the months. One day while playing with the youngest one I opened the compartment of the little push car (that had been moved in from outside and was temporarily in the living room, then went to the basement) and there were my keys! My 4 yr old had used them to "start the car" and then placed them in the compartmenet. I also found my leather flip flops after months in the play "dryer"... My suggestion - look in all the places your kids play - dress up clothes, etc.
I know someone who went out to dinner and when she thought she was grabbing her cell phone she was actually putting the TV remote in her bag. The babysitter couldn't find it and when my friend attempted to call the babysitter to check in she pulled the TV remote out of her bag!!!!
(Did you look in your freezer - stranger things have happened!)