I finally upgraded my beloved Sony Xperia Z1 Compact D5503 Android Smartphone (Black) International Version No Warranty. And while it still works, I've had to replace the battery and while trying to replace the front outer screen, I broke the LCD screen. So while a new screen was on order from Hong Kong, I decided it was time. I bought the brand new Xperia XZ1 Compact.And wow, this thing is expensive! What could it possibly do that my older Z1 Compact couldn't do already? I was skeptical.T-MOBILE: I am on T-Mobile and had to switch from a larger sim card (micro) to the smaller card (nano). I quick trip to the local T-Mobile store solved this easily at no cost to me. Once the sim was installed in the phone, and booted, both WiFi-calling and voice-over-LTE worked automatically. There was no configurations steps that I needed to perform at all to get this to work. It also displays an icon to prove to you that it is enabled. And the reception on this new Xperia XZ1 kills the original Z1. I get LTE reception is areas that I get no reception on the original. Again, this makes the upgrade well worth it to me.PHYSICAL DESIGN: I really miss the physical lanyard loop in the lower right hand corner of the original Z1. I used this feature a lot. It let me grab my phone out of my pocket with zero chance I would drop it. As the years went by I use it while hiking, while navigating the streets on foot, while stumbling, fumbling, and slipping. Not once did I drop it. Or at least when it did slip through my fingers unintentionally, it caught on the strap - It was always strapped to my wrist like a camera. Now that feature is gone. And I will surely drop this new XZ1 Compact before it is all said and done, it is only a matter of time.The XZ1 Compact is larger than the original (see comparative photograph). The screen is also physically larger when powered on, although the resolution is identical. The corners are much sharper on the new XZ1 also. This makes the phone slightly more uncomfortable in my front pants pocket. The corner of the phone puts more concentrated pressure on fewer threads of my pants, causing more wear and tear over time. Again, not as well designed as the original.I like the power button, even though the fingerprint scanner has been disabled in the US model. Fingerprints are not a very secure method of entry anyway. The button is indented and your thumb fits into the groove perfectly. It feels great. The plastic volume rocker up above it isn't as great though. Rubbing your thumb up the side will catch the button sharply, it doesn't feel good. I liked the original metal Z1 volume buttons better.Another designed choice I don't particularly care for is the USB power entry on the bottom of the phone. Why the bottom? I sit my phone in the cup holder of my car, and like to charge it during the ride while listening to Bluetooth music. Now I can't do that. There is also no way to rotate the screen completely upside down either, only landscape. Score another win for the original Z1 design.SOFTWARE: I miss the Album widget! I now must open up a dedicated app to see my photos, where before I could just scroll from the Android screen widget. Maybe there is a way to get this back by downloading it from Sony? Regardless, it is not installed by default and I didn't see it anywhere. And at least one of my favorite apps, Samsung SleepSense, doesn't work at all on the new XZ1.I have to comment on the original "Rings" theme that comes installed and active by default on the new XZ1. It is very cool and consistent with Sony's past theme offerings (Playstation, Xperia). When you push the power button on the side of the phone, the screen comes on but is totally black. And the OLED technology means that black looks off - no light. But colored rings radiate from where your button pressed, This is a very cool effect and I haven't got bored of it yet! I love turning this phone on just to see it. From the normal Android screen, you can touch any area without an icon and more rings radiate from your touch. When powered from a USB source, the rings radiate from the USB cable instead. Super cool!The Playstation 4 remote play works well. I can boot my PS4 from sleep mode over wifi anywhere in the country, and a easily paired PS4 Dual Shock controller allows me to control the action. A small Miracast adapter like this (TAIR 1080P WiFi Wireless Mini Display Receiver Dongle HDMI Adapter TV Miracast DLNA Airplay) ensures that you can use a larger screen that has HDMI inputs - like a hotel room. PS4 on the go via the new XZ1 Compact. Cool.DISPLAY: Wow, the TRILUMINOS LCD screen on the new XZ1 Compact looks absolutely brilliant! It is by far a much better technology than the original. It looks breathtakingly stunning. I love it! The blacks are completely absent of light, and the rich color gamut is deep. Everything looks much better on this new XZ1. The faster processor also makes the screen amazingly responsive. And the new Android Oreo transitions animate very fluidly. Beautiful!CAMERA: The camera is also better. Although I haven't had the chance to experiment with the 960 frames per second and the 3D scanning technology yet, I am looking forward to it. This is just not technology that is going to be used very frequently though. But the camera and 4k video will be, and so far the XZ1 camera technology far outpaces the original Z1.AUDIO: Listening to music on the new XZ1 Compact sounds awesome! I can't believe the front firing stereo speakers on this new phone. The acoustics of the XZ1 Compact are on par with higher end battery powered portable speakers. Listening to Lana Del Rey's Lust For Life [Explicit] sounded brilliant, with very crisp and clear mid-tones and treble, and surprisingly present amounts of deeper bass. I'm amazed! I never felt like the original Z1 was an acceptable way to play music using only the internal hardware. But I'll happily enjoy the new acoustics XZ1 when convenient. This alone is worth the upgrade for me.CONCLUSION: There are definitely design features that are better done on the original Z1 Compact. The original Z1 Compact is a great phone that has held up well over the years. But all the new technology on the XZ1 Compact is absolutely stunning... the better reception, WiFi calling on T-Mobile, the amazing acoustics on the front firing speakers, the camera, and the beautiful IPS LCD screen. I can't believe all this tech fits into such a small footprint. The winner by unanimous decision - The new Sony Xperia XZ1 Compact! Highly recommended.