I've just bought the PANASONIC-KX-TG8524EB 4pack of dect phones for £103.30 from Comet, store price £134.99, web price £111.44, but on the webpage there's a banner saying:
"Save an additional 10% on all landline phones when you use the voucher code "10LAND" at the checkout"
So this code should work with all landline phones, it worked for my purchase, to discount the web price. I can't find start or end dates for the code.
I paid £100.30 using 10% off with "10LAND" and on top of that £3.01 due from Quidco.
Free delivery offered, although I picked mine up because delivery slots were too far in the future for me.