You can buy a Applico modem/fw which has support of Dynamic DNS and get s you a DNS name even with changing IP. Applico systems updates the dynamic DNS automatically. It is also a SIP proxy, server, NAT traversal , DHCP systems etc. You can have at least 5 SIP systems behind it. Your IP phone (grand Stream is the cheapest) or buy a cordless WiFi phone since Applico systems also support WiFi.
NO need to get a vendor (telephony VOIP) you become a home telco. You can also attach a telephone line and if you do not answer the call it can also forward to you mobile phone.
If you need more information send email to me at
[email protected]