I transferred my number from Mint Mobile to Visible 8 months ago or so. I tried to at least. They initiated the number transfer before accepting payment from me. Their iOS app was bugged and their web app had no way to pay. I engaged support and they escalated to engineering. Still had no phone number or cell access for 3 days, with an upcoming trip planned. Ended up getting them to transfer it to US Mobile which has been fine. Probably works a lot of the time but it’s a shitshow.

On the upside, your phone can be thinner now and the down time gives you, the chance to admire its aesthetic without distraction.