The device Ash uses is a Telecommunications Device for the Deaf (TDD), sometimes referred to as a teletype. The device has mounting cups on the top for old analogue telephones, but many can connect to mobile devices. They are still widely used where mobile data or internet connectivity is limited.
Ash doesn't speak until the 30-minute mark.
The envelopes Sarah uses to mail the documents and fee are addressed to Archie Leach, the birth name of Cary Grant.
The Americans with Disabilities Act prevents the relay operators from disclosing any information. They're saying the calls are not recorded. There are no records, so it's very untraceable. It's old analog technology. It's now being replaced by new stuff, but it still exists. The relay services still exist, but that technology is what Riz's character, Ash, uses to try and stay ahead of people who are able to track his digital footprint.
Over 50% of the movie was filmed in New Jersey.