Escargo Express is a storage company. In short it will keep all your items for you for a small fee. They will deliver an employee to take or get up to three items in your storage.
To call Escargo Express, call Ness' mother at Onett and she'll give you Tracy's hotline. Then call Escargo Express to talk to Tracy. This is one way to dump all your useless items and key items you no longer need.
The comapany building itself is never seen in the Game.
 Sound Stone Trick
The Sound Stone is given to Ness by Buzz Buzz and can never be removed from the inventory, even Escargo Express will not take it but there is a way to leave it with them: First before going to the meteor defeat as many Spiteful Crows as possible they will fill your inventory with dropped Cookies, if your inventory is full, Buzz Buzz will give it to Tracy which you can pick up from Escargo Express when you need it.