If your RJ9 headset is compatible with following phones with standard RJ9 port, and you want to connect the headset directly to a 2.5mm headset jack this adapter will work. Compatible List(Part): AVAYA / Lucent: 6402D 6408D+ 6416D+M 6424D+M 8403 8410D 8434DX 4406D+ 4412D+ 4424D+ 4424LD+ 1120 1140 1165 1210 1220 1230 1408 1416 3904 3905 7208 7316 9404 9406 9408 9504 9508 2410 2420 5410 5420 5610 5620 5621 5625 DT1 DT3 DT5 QE4610 4610 4610SW 4612 4620 4620SW 4621 4621SW 4622 4622SW 4625 4625W 4630 4630SW Aastra: 2465 2564 480 480e 480i 51i 53i 55i 57i 57iCT 554 564 565 i733 1120e 1140e 1150e 1210 1220 1230 i2002 i2004 i2004 IP i2004 Phase II i2052 7406 8540 9617 6730i 6731i 6739i 6751i 6753i 6755i 6757i 6757i CT 7446i 9112i 9133i 9116 9143i 9480i Dialog 4222 4223 4224 4225 M2216 (ACD I or II) M3905 M4000 M4020 M7208 M7308 M7310 M7316 M7324 M4000 M4020 M5208 M5209 M5216 M5317 M7900 M8001 M8003 M9009 M9516 Powertouch 480 480e 480i i2002 i2004 i2004 IP (not for i2400 phase II and i2004 POE ) Allworx: IP 9112, 9204, 9212, 9222, 9224 Adtran : IP321 331 430 650 670 Alcatel-Lucent: 4004 4020 4022 4035 4037 AltiGen: 500 510 600 705 710720 Ascom: Berkshire 200 400 600 800 SD30 MR30 51 61 Comdial: 8312 8412 Digium: D40 D45 D50 D70 Gigaset: DE310 DE410 DE700IP DE900IP InterTel: 8520 8560 8600 8620 8660 8662 8690 Axxess Basic Standard Excutive Mitel: 5000 5010 5020 5040 5055 5140 5201 5205 5207 5210 5212 5215 5220 5224 5230 5235 5240 5250 5312 5324 5330 5340 5550 SuperSet 4015 4025 4125 4150 Plantronics: A100 S10 S11 S12 S50 T10 T20 T50 T100 T110 SP-02 SP-04 SP-05 A100 T50 T100 PLX-400 PLX-500 MiVoice: 5312, 5320, 5320e, 5324, 5330e, 5340e, 5360 4222, 4223, 4224, 4225, 5370, 5380, 8528, 8568 6730a, 6730a