I think they caught on with those SMS apps like textnow and such, so the only way is to get a cheap pre-paid sim card with no credit on it. I think you can get them for like $1 or 2. And should be able to do a couple of accounts with that.
If it's on account creation, there is or was a method of creating Google Accounts without a number. Get Google Chrome, click on your user, "manage people", create a new user and when it tells you to sign in, make a new account through that. Though it's been 4 months since I've done it last so I'm not sure if they caught onto that as well. But I made maybe 50 accounts through it in the course of a year and never got asked for a phone number.