Probably old news to everyone, but if you use your smartphone a lot in the course of the day there’s a rig that makes hands-free use comfortable, convenient, and less-annoying for whomever you may be speaking to.
A single wire with one earbud and a mic works well. Excellent call quality, especially when compared to speakerphone or a bluetooth earpiece (and probably less bio-hazardous than the latter). And the single earbud allows the other ear to stay tuned into your surroundings.
This particular one is in my experience a good buy.