Can there be any justifying reason to track messages on a smartphone?
People want to track their phones on the web to keep an archive of their texts and other media. Parents who are concerned about their child getting bullied in school want to track their conversation online. All these are justifiable reason to have your phone tracked.
What can you track, iMessages WhatsApp messages or text messages?
Both instant messages and text messages can be tracked, but it really depends upon the sophistication of the spyware. Usually, the premium version of these apps allows you to access even all the media file of the phone let alone the texts.
How to start tracking?
The most important step is to install the application in the target device. Instead of tricking the users to install it by himself, you will have to get physical access to the target device. It will take a few minutes. The app will go in clandestine mode after installation. The user is not going to find any clue of it as it will invisible even in the app installed directory.
What is the best app for tracking?
There are multiple applications available for the tracking. Some are free with limited functionalities while some may cost you a little money to unlock all premium features. I would personally recommend you to buy from the company that provide apps for both platforms. So if you are using it to track your kid, and if he/she happens to change the phone, you can still track them on the web. Also, the app should be able to track all messages: texts and instant messages. Plus, it must be able to retrieve deleted messages.