I like the use of round bubbles for photos and the squares used for the messages/text.
UI/UX Works by Jakub Antalík | Abduzeedo Design Inspiration
Kama - Mobile UI Kit by isavelev.com on Creative Market
National Geographic Mobile
Adobe Photoshop UI Kit — Free Download
Showcase and discover creative work on the world's leading online platform for creative industries.
DO: Free App UI Kit for Photoshop & Sketch