… Why? Because they have the same “Memory Stick Duo” card slot!
… You can use these phones to move files around and listen to or watch the stored music and videos from either device. — While the PSP has a larger screen, these small phones are great for audio.
You can even take photos on the phone and then view them on the PSP, or use your phone's web browser to download content when you're not near to a Wi-Fi hotspot. — Very cool combination! 👍🏻