Finn's phone is a phone identical to an old handheld radio. It has stickers of kittens and the word "SHMOW" on it. The knob can switch pictures of faces to whomever Finn wants to contact. It first appears in "Go With Me." However, Finn is seen with a different phone in "The Pajama War", implying that it might've been replaced.
At present, there are three known contacts in the phone:
Since Finn's contact for Jake is on his phone, it means that Jake's phone has another contact, Finn.