How and where do liveaboards, who does not own or maintain a shoreside residence, establish a legal residence for the purpose of 1)Taxes, 2)Voting, 3)Driver's licenses, 4)Car registration, 5)Boat documentation, 6)Phone/internet service, 7)Mail, 8)etc.?
In my previous post I failed to address the phone/internet issue you raised. I suspect most cruisers will have cell phones. As a (much less expensive) alternative we also have VoIP (voice over internet protocol). Basically, whenever we have an internet connection (eg, WiFi) we simultaneously have phone service via VoIP. It costs about 1 cent/minute to call anywhere in the US and slightly more abroad. You also pay $3-5/month for a dedicated phone number (to receive calls) depending on the area code you select. You are typically not charged for incoming minutes unless you exceed several thousand minutes per month. We use CallWithUs and Future-Nine. Both are very reliable. For further information here are their websites:
Build Your Own Service Plan
VoIP Phone Service | Internet Phone Service | Cheap VoIP Provider | Pay As You Go VoIP Service
Relative to the mail forwarding service, we try to setup a separate address (eg, with a family member) to receive bulky stuff such as magazines and catalogs. The reason for this is you must pay to have mail forwarded and the cost can skyrocket as the weight climbs. This has nothing to do with your domicile, but it is something you may wish to consider.
As an aside, I wonder if the OP has lost interest in this thread since it has drifted pretty far afield from his original question!? Personally, we would like to help since we have previously addressed the very same issues.
Hope this helps.