Recently, I've buy a "new old stock" Cisco CP-6921 in order to replace my old POTS phone used in conjunction with my FXS that I've configured not long ago. So, as Cisco do their best, it's not straightforwardly to configured without their proprietary softwares. Fortunately, there's tons of resources to help and, finally, got me through and got it done. So, to help alleviate the pain that I've gone through, I decide to, once again, write this memo.
This is how I done, not a tutorial. Use your own discrestion. I won't take any responsibility if things break.
