My 9 and 12 year old share a "kid" phone that's just a hand-me-down parent phone. This partially meets that need, but it still gets used for way too much unsupervised YouTube time.

The thing for me that has really unlocked voice-based socializing has been the 12 year old jumping on Discord with his buddies from school. I feel like this mirrors well how I myself chat with my adult male friends—it's rarely in the context of just "a call" but rather while doing another activity. So when I see him joking around with them while they play Minecraft or whatever, that feels like it's a reasonable pattern for how to sustain friendships.

My kid uses a shared Google doc to chat with friends on their school-issued Chromebooks. (But still has the problem of unsupervised screen time.)