iosiphone
I'm using iPhone 4 (iOS 7.x.x). I tried doing video call using WhatsApp and few other video calling apps. But it didn't support video call.
Is it a limitation of iPhone 4? Or is there any possibility to resolve the problem?
FaceTime is working but is it available for Android phones?
(See @stuffe's answer on how to install apps onto old versions of iOS)
The short answer is there is no way to install an app that was created for an iOS newer then the one you are running. You should connect the device to iTunes and see if you can get it updated to the latest 4.x iOS as many games and apps that target the 4 to 8 year old demographics will certainly work on that older OS.
The longer answer (and some related discussion on this site) is that developers of more powerful apps want to use the latest APIs that are introduced every iOS, and for a developer to create an app for an older iOS version, would mean he couldn't use the newer tools. Worse, it's more work to keep using the older API so cutting them makes schedule and financial sense. For example, a resource known as ARC (Automatic Resource Counting) has made a huge difference in reducing the time and cost of app development by automatically doing things that otherwise the developer would have had to manage.
Because these necessary APIs don't exist on pervious iOS versions, there is no way to run a newer app on an older iOS. Hopefully you can use the web versions or find acceptable apps to do the things you need this device to do to continue to be of use.
Ok, figured it out myself. My first problem was that for some reason my phone hadn't activated properly with iMessage / FaceTime (my phone number was unchecked in the You can be reached by FaceTime At section in FaceTime settings). That required switching off FaceTime and iMessage and switching them back on again after a short wait so that they could activate properly, which they did.
Once that was done, my FaceTime settings (on my iPhone) had a new option: iPhone Mobile Calls:
My wife's phone also has that setting. Choosing which phone is used is just a question of only having this setting enabled on one phone at a time. I assume (all though I haven't tried it) that if both phones are enabled in this way, FaceTime on iPad or Mac gives you the choice of which phone/number to use. It wasn't giving me a choice earlier because there was only one phone enabled.
Best Answer
Although WhatsApp is compatible with iOS 7, the video calling feature requires iOS 8 or later.
FaceTime is available only for Apple's iOS and macOS. You can make a FaceTime call to your contacts using iPhone/iPad (iOS 7 and later) or Mac (OS X 10.9.2 or later). It is not available for other mobile or desktop platforms.
There are various other popular cross platform messaging apps with support for video calling (Viber, Hangouts, Google Duo, Skype) but they all require iOS 9 or later to be installed.
You can give Zoom a try. It claims to support iOS 7 and later.