Plantronics CS540 and CS55 headsets disconnect after 30 seconds

[Etch]

Hello everyone. We have about 5+ CS540 headsets as well as CS55 headsets as well. 

For awhile now, every now and then the headsets will disconnect after about 30 seconds. The call will resume, its just the headset that disconnects. We use cisco CP-7841's and have verified that the hookswitch control is enabled on every phone. 
Our fix has been to resubscribe and reboot the phones and on a few other occasions replace the phone. We have done this for multiple devices, and it usually works for a period of time, but we keep coming back to this problem. Any suggestions or help would be greatly appreciated.

PS: we do not use cisco unified communications management. 

[Mohammed al Baqari]

Look online for cisco tested handsets and supported firmware to makesure
that you aren't running into incompatibility problem

[Bobby Stojceski]

That's strange, what you're describing is the classic "Electronic Hookswitch Control" issue but you said you have enabled that already. be sure to check the switch on the underside of the headset's base station to ensure you have it set to the appropriate numbers for Cisco handsets. Be sure that you have applied config on the handsets after enabling hookswitch control as well. A reset never goes astray either.