Just saw the story on WBUR about this project to alert people about immigration raids:WBUR story: Text Messages In Somerville Would Warn People Of Federal Immigration Raids
That links to the Somerville Journal piece with more: Rapid Response Network to provide ICE updates in Somerville
But the full details and the 2 phone numbers you need are on this page of instructions. There's one number to get alerts (617) 941-3812.
NOTE: there's a different phone number to report raids (617) 863-7783.
http://somervilleresponse.org/