What are usually considered the essential components of a smartphone?
Here is list of common features found on most smartphones
1. Operating System (OS)
2. Phone Camera
3. Battery Life
4. Connectivity Options (Wi-Fi, Bluetooth etc.)
5. RAM and Processor
6. Storage Capacity (Internal/External)
7. Speaker Quality
8. Display Type and Resolution 
These can vary from device to device based on factors such as budget, brand and preferences.