Are there cross-platform mobile messengers without number binding for iOS and Symbian?

Question

Mobile development

Hello,
I am looking for a messenger so that it does not require binding to a number or a sim card and can be installed on iOS and Symbian 9.3/9.4. Needed to talk with elderly parents in another country using an old iPhone (I have a Symbian phone).
Mandatory:
- text messages
- voice calls
- clear interface
- availability in the Apple Store
- without reference to a number or a SIM card
Desirable:
- video calls
- file transfer
- desktop or web client
Don't care about popularity, the audience is already prepared.

Answer 1

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