Some Android devices have an option to restrict notifications or background activities of apps due to battery optimisation features. Please make sure your battery optimisation function is off if your device has such feature. Also, please make sure you enable floating and lock screen notifications.
Yes, Just choose "Show iPad & iPhone Apps" in the iPad App store.
Yes, it will work on all SIM cards.
Currently, only Voico, UAE, HiU Messenger, BOTIM and C’Me meet UAE regulatory framework requirements to offer VoIP calling within UAE. New VoIP apps may be added to the list of supported apps once they meet the requirements.