They had a People hub that collated all your contacts and had reasonable sharing mechanisms for the data. HERE was essentially that places concept. I'm sure if Windows Phone had kept traction, it would be integrating your smart device health data into live tiles and a hub interface for all the metrics.
* let’s keep it time accurate :)
Nokia's maemo had this done with better execution. The SMS app had a plug-in for xmpp and I used it for Google talk. I think I used a third party one for Google voice. There was a Skype one that supported calling through the normal phone app but it didn't work very well. The clients were run on the phone and not in the cloud.
WP8 relaxed some of those restrictions but it wasn't enough to truly develop a IM client.
It's true that only Microsoft could create such integrations, but it was a business decision. On Windows Phone 7 era, regular developers couldn't deploy native code and you couldn't call native APIs directly from the managed .NET/Silverlight runtime. Native SDK wasn't available at all, but it was a regular Windows CE at its core.
Maemo's was way superior to Windows Phone. It's a shame that Microsoft trojan-horsed Nokia.
In this world where we expect internet access, I'm beginning to think OSs need to manage certain types of data more proactively. I'm trying to wrap a general point around your concerns about contacts. Contacts seem one of the data types that need something approaching OS level tooling. For me, another is "tags". I want to use the same set of tags I apply to "files" to apply to "contacts" too.
I keep hoping someone will make a rival OS that tackles this head-on. Start at Haiku, sprinkle some of Apple's "the UI isn't a virtualised office any more" UI paradigm, model a small handful of human-centric data types (like places, people, maybe individual health, too) and the access and interaction rules that support them safely and really run with it.