Apple iOS - closed Ecosystem
The only Alternative to BlackBerry 10 OS
Apple's ecosystem is similar to that of BlackBerry - to use an iPhone and the manufacturer's services you need an Apple ID, so you have to register as a customer with the manufacturer. Data backup and synchronization of smartphone content with the local computer is only possible at no extra charge via USB cable using iTunes, a desktop software similar to BlackBerry Link. A great alternative to iTunes is iMazing by DigiDNA, which is available for macOS and MS-Windows.
Data Backup local or cloudy
Personal data and software of the iPhone are synchronized with the PC, notebook or Apple computer via USB cable or WLAN or wirelessly synchronized with Apple's iCloud (if desired, automatically after connection to the charger via WLAN overnight). Apple's iCloud runs in data centers of Amazon and Google.
Wireless data backup in Apple's iCloud is more convenient. Commercial users and private individuals who want to protect the privacy of their stored contacts use only the local computer for data backup!
No USB Mass Storage Mode - File Management limited
iOS does not provide free access to the file system and therefore does not offer a USB mass storage mode like Android, which allows you to access the smartphone memory via cable from the PC. If you can't accept the restrictions listed so far, you shouldn't get an iPhone. I was sceptical at first because you depend on the reliability of the syncing software. Compared to the previously used Nokia PC suite, the Samsung Kies doesn't run on my notebook, and BlackBerry Link that is hostile to the user, Apple iTunes is much better (addendum 27.05.2018: and iMazing by DigiDNA also crashed at first). Since I don't use iCloud or Apple Music, no music files were deleted or messed up. This was temporarily the only serious bug in iTunes.
Even with iOS version 12.3 no free Access to all Files
MS-Windows offers the File-Explorer and macOS the Finder. iPhone and iPad got an app called Files on 19.09.2017 with iOS 11.
But even with this, Apple customers have no free choice where to store their data. Files can only be synchronized with the iPhone by storing them in specified folders on the computer. Ideal for technical laymen, but advanced users feel patronized, want real access to the file system!
iCloud: Transport Encryption finally improved after 3 Years
05.08.2016: The online connection to the iCloud (icloud.com) did not offer good transport encryption so far. This has now improved considerably. Check for yourself with the SSL Server Test. (Rating "A+" would be perfect, currently the iCloud reaches "A" after all).
Update 17.05.2019: While revising this report I also made a new SSL server test. Apple has again improved the transport encryption significantly!
Apple has the iCloud keys and gives out customer data against court order. American companies have to do that (Patriot Act)! BlackBerry (Canada) does not wait for court orders, but actively reports suspects to the authorities. Tim Cook/Apple wants to make the iCloud more secure (sometime no more keys at Apple) and we will see how far the American government tolerates this. Then really only the end customer with his key could access his own data.
Tim Cook fights for Privacy and against Backdoors
Apple's CEO is supported by a number of large companies and decision makers and plans to secure the iCloud in the same way as the iPhone.
With iOS version 8 Apple brought data encryption to the iPhone. The communication between iPhone users via iMessage is end-to-end encrypted. iMessage is a messenger like BlackBerry's BBM Enterprise (formerly "BBM Protected", but only business customers can book this via a system house).
Note: with iMessage, no one can access your communication data as long as you avoid using iCloud as a backup medium!
References: Apple iCloud uses Amazon AWS, Google-Cloud and Microsoft Azure: ifun.de, Onlinehändler News.de, t3n.de, flat.de. Test transport encryption of the iCloud yourself: Rating of Qualys SSL Labs.