It will be fine for text and voice between maybe 2 people, You really need to test and find out. The problem is voice services and anything doing live transcoding can be CPU heavy and most likely why they are recommending 2 CPU cores (2 cores are on the $20 droplets).

I was reading conversion on the official blog of Discourse and it was commented there:

“The only time you typically need swap is during the /admin/docker upgrade process. And Sam’s recent Sidekiq upgrades free up about 7% more memory on top of this.
1GB is a 100% officially supported install now, the swap file is just a bit of insurance! ”

I think it will be safe to use $10 droplet.