C300A in, working fine. Minor niggle how flimsy the battery cover seems when you install the batteries and close it, a bit worrying but once done it's secure enough.
As expected the ADSL filter presented no problems, in my opinion there was a confusion with other models with VoIP capability.
Regarding sound quality, incoming speech is perfectly audible but noticeably less distinct than even my old Binatone, it accounts for the reports of being muffled but I don't think it's too bad. Not worth rejecting for some Panasonics anyway - especially as I like the styling and particularly the display. Where it does score is the outgoing sound (although it is difficult for me to experience it myself) is reported as very good - much better than the Binatone (for which I received complaints) and the Phillips (which was worse).