Annie,
it would be better if you posted in Parents Emeritus, especially as your son's main issue is mental illness. My son (20) is also bipolar, also has burned through his SSI at various banks, also is homeless (2 years now, lives under a bridge).
Here is the thing we in Parents Emeritus work on coming to terms with...we cannot make them become normal. We cannot make them be who we want them to be. We cannot make them take care of themselves, take their medications, make good choices, save their money, get a job, a roof over their heads...none of that.
We can...take care of ourselves. We can refuse to engage in threatening ugly or abusive conversations, by text or otherwise. We can learn to not let wondering where he is or how he is disrupt our days and nights, our much needed sleep.
YOu have taken a big step simply by knowing he cannot live with you. That is a struggle for a lot of people here on the board, and you have already done that. Take another, little step. WRite down a few things to say if he is ugly when he calls....how about "I'm sorry, I won't be talked to that way. Lets talk again when we can have a better conversation" and hang up. or "I am not willing to listen to this. We'll talk when I am in a better frame of mind and you can be civil" and hang up. Don't pick up again for 24 hours at least (be prepared for the phone to ring and ring and for him to be angry)
To texts..."PLease don't send me ugly or threatening texts. I'm turning my phone off now. I won't accept or respond to texts like this anymore". Then turn your phone off for a while. If you can't do that, figure out how to block his number, which is possible in most cases.
You can add "I love you but" to the beginning of any of those responses.
He will likely escalate both in frequency of texts and calls and in abusiveness. HOld the course. Hang up each time. Do not tolerate being treated that way...by ANYONE.
Echo