If you're in the US you can get a real cell phone number with VoIP and SMS that works without a phone for $20/mo with Google Fi. You'd need a phone to set it up but after that you could just turn it off and still use VoIP and SMS from any web browser.
There are BYOD prepaid providers that are even cheaper than that. The lowest you can get is ultra mobile's $3.50/month plan, but you need to jump through some hoops to get it working, like getting a physical sim in person. Tello is $5/month and you can activate online.
