IPv4 addresses are slowly running out. As a consequence a number of ADSL and cable network providers have now started to give customers non-routable private IP addresses and perform Network Address Translation (NAT) at their border gateway to the rest of the Internet. As the NAT is performed on their turf they call it Carrier Grade NAT or CGN.
While being state of the art in wireless networks for many years now CGNs certainly have one advantage, they shield mobile devices from unsolicited packets from the Internet and hence keep power consumption down. Unfortunately there is a major disadvantage as well which is especially troublesome for fixed line connections at home: Your network is not reachable anymore for incoming connection requests.
Many people won't notice but as soon as you are running your own services such as an Owncloud server you are out of luck. Verizon, for example, is switchng to CGNs and private IP addresses and some German cable operators have started doing it as well. While Verizon at least offers a way to opt it seems that others are less flexible. Too bad when you signed a one year contract… I wouldn't be surprised if some will even start asking for extra money for a public IP address. Market economy, scarce resources, you get the idea…
IPv6 is obviously the solution but networks, devices and VPN gateways supporting it are still scarce. Therefore make sure before changing your home network provider that you will really get a public IP address!