It would be nice if the iOS and Android built-in Contacts apps had better support/integration for all the various messaging apps that work on their respective platforms. Rather than trying to remember who uses which services, their contact card could simply contain the entire roster of their services and usernames, and you could initiate a conversation in that service from within the contact card. I know you can do this with the baked in messaging services for each platform (SMS/MMS and iMessage for iOS, SMS/MMS and Hangouts for Android), but I'm talking about a one-stop-contacts-shop for every major messaging platform. Maybe that would require too much cooperation between messaging app authors and the big OS vendors, but I think it would be possible.

An alternative solution would be a cross platform third party Contacts app that offers that kind of integration. I've seen multi-messenger apps (Trillian, IM+) for both platforms, but that's not quite the same thing and it inevitably leaves out important functionality from the official apps.