There is no shortage of messaging apps and features on the Xperia Z1S, and more so in Google's Play Store.
To start, when we talk about messaging, there is SMS or text messaging. On the Xperia Z1S, as it is with most Android 4.3 devices, your contacts would be connected to your Google account. When using any Android device, it's imperative to have a Google account connected to the device so you can download apps and use most of the phone's services.
The default messaging app is painfully simple to use, and is like any other smartphone out there. Messages are threaded and divided by names or groups, and to start and delete new threads is easy. You simply hit the write button, or press and hold a thread to delete.
Another choice you'll have - and one I recommend - is the option to merge SMS messaging with the Google Hangouts app. If you choose to do so, Hangouts will become your default messaging app when it comes to SMS or actual Google Hangouts.
It takes some time to get used to having Hangouts as your default SMS app, but once you get the hang of it, it makes everything feel a little more streamlined. Some might prefer to keep the two separate, but it's worth noting that, like the Nexus 5, you have the option to do that here with the Z1S.
It wouldn't be an Android device if the default e-mail client wasn't Gmail, and it works quite well here. You'll get push notifications for all your e-mail if you want, and you'll have the same organizational options that you would on the desktop client.
If you want to star, archive, delete or move messages and threads, you can do so in the Gmail app and it's all very intuitive. Power Gmail users might wish for more, but it's great and more than does the job. Besides, I tend to think of e-mail on a phone as a tool for quick interaction, and not a place for writing love novellas to your distant lover.
There are more messaging apps in the Play Store, like Messenger for Facebook, or WhatsApp, Line and Kik if you want to send more than just messages. The last three apps will allow you to send text, voice and picture messages to anyone using the same apps anywhere in the world.
As long as you have a data connection, as a WhatsApp users, for example, you'll be able to send other WhatsApp users messages anywhere in the world at no additional cost. Shop around and see which app is best for you. Best of all, they're free or very inexpensive to download.
While we're on the subject of messaging, let's talk about the default keyboard for the Sony Xperia Z1S. In short, it is great. It's so much better than the stock Android keyboard, and more than holds its own against third-party keyboards like SwiftKey and Swype.
The closest keyboard I can compare it to is Swype, but I think I may prefer the Xperia keyboard just a little more.
It's worth taking the time to learn how to swipe around to enter text than it is to peck away at a screen. It will improve your messaging time dramatically, and it makes sending messages and writing notes a pleasure, rather than a chore.
No harm in going for what you're used to, though, but I highly recommend giving the default a try for a few days before you go splurging a few bucks on Swiftkey or downloading and installing Swype.