do they make one of these? How about a cordless phone?

Z:
Poor man's cordless headset. If they have S/L card or adapter. Make that port ring on any line that rings your clients' extension or put both into hunt group. Use a Plantronics CS-12 --single line phone/headset. Works pretty good in most environments. Cheapest way to go if you have the S/L port open. Retails at Office Depot for around $127.

nec makes a 16 button dtu style cordless phone. it is a stupid design. there is NO keypad on the handset so you'll still need to be close to your base to transfer calls. uses a standard digital phone port.

there is also a 4 button cordless phone. it has the keypad on the handset as well as 4 programmable buttons on it as well. it can either go inline with a desktop phone (and be switched to the cordless when necessary) or just be put on a digital station port. if you use the switching method just know that the 1st 4 buttons on the desktop will be the same a the 4 buttons on the cordless. you can hold, transfer etc from the cordless.

both of those options run around $350-500 and the range isn't great. about 150'
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you can get a plantronics cordless headset with automatic handset lifter thingy. still pricy tho.