Observant types testing early builds of SOCOM: US Navy SEALs Fire Team Bravo for PSP have noted a headset icon on the game's HUD, suggesting that we'll be able to buy a headset and partake in voice comms when the game's finally released.
Further to that, Kotaku's since produced a photograph of what looks like an official Sony PSP headset peripheral - two over-ear headphones with a microphone extending from the left.
As fans of the PS2 series know, voice comms plays a big role in Zipper Interactive's tactical military strategy-'em-up, so it's hardly implausible. We already know Sony's quite happy to meddle in PSP peripherals, iterating the battery technology and including a microphone peripheral in forthcoming translator tool/game Talkman.
Sony Europe doesn't currently list a release date for SOCOM PSP, but the game's due out in the USA on November 8th.