Cyanogen users will soon have access to a special version of Cortana for Android, coming to the One Plus One later this month, and other Cyanogen devices early next year. Microsoft entered a partnership with Android ROM vendor Cyanogen earlier this year. You can write an SMS to reply to the caller on your PC, and through the power of Internet syncing, the SMS will get sent to the caller from your phone.
Missed call notifications are similarly Android- and Windows 10 Mobile-specific: miss a call on your Cortana phone, and your Cortana Windows 10 PC will tell you. On iOS there's no hands-free voice activation at all. On Android, "Hey Cortana" voice activation is supported on the Android home screen, but not system-wide. Neither iOS nor Android supports opening apps or changing settings from within Cortana. There are some differences in capabilities due to the API availability of the respective platforms. Cortana requires a Microsoft Account to use, and will sync your various interests and settings between all Cortana-enabled devices. Those cards can show appointments, track packages, give you weather information or the latest sports scores, and so on. The Cortana app looks essentially the same whether on Windows 10, Windows 10 Mobile, iOS, and Android search box at the bottom, hamburger menu on the top left, and information cards. The version shipping today isn't hugely different from what we saw in July. We looked at the Android preview when it first came out.
Enlarge / Cortana's appointment and flight tracking.