Body Presence, Dedicated Home Office
It's common for Home Office workers to feel that if they do not answer the phone immediately they will be presumed to be shirking elsewhere. Which is ridiculous because Office based personnel go awol just as much. What I would also suggest is some form of SLA for your contact time defining an acceptable set of core hours when you are readily accessible and agreed response times to missed calls and replies to emails.
I'm lucky in that we were able to split the garage to give me a dedicated 3m*2m 'office'. Fully loaded with all the essentials of wired network connections for the PCs and the Cisco Phones, printers and space for books and work in progress paperwork.
The only change I would make is to have a wireless handset on the works phone, then you don't feel tied to the desk during office hours for customer calls