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Cisco SPA504G 4-Line IP Phone with 2-Port Switch, PoE and LCD Display 1 x RJ-7 Headset, 2 x RJ-45 10/100Base-TX , 1 x Sub-mini phone Headphone | Canada Computers & Electronics
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Amazon.com: VoiceJoy Headset Headphones with Volume+Mute Control+Standard 2.5mm Plug Jack for Cisco SPA Series Spa303 Spa504g and Other, Polycom Soundpoint IP 320 330, Grandstream, Linksys,Cortelco : Electronics
NEW Sale 2.5mm Plug office headset Anti-noise Headphones with 2.5mm plug for Cisco Linksys SPA501G SPA502G SPA504G GIGASET - AliExpress