You can read more about the change at the blog post below, but the bottom line is that free accounts are going away after 7 May. If you want a free alternative, No IP is still a solid option.
Some routers and devices only support DynDNS, though, and if that's the case, it's worth paying the $US25 per year — it's not that expensive considering what you get. You may also be able to install DD-WRT on your router, which supports No IP.
Check out DynDNS' blog post below for more info.