The area code 857 is located in Boston, Massachusetts.
Area code 857 serves Boston, Massachusetts, and the close-in urban core around the city. It is an overlay of the historic 617 area code, created when the region needed more phone numbers due to growth in mobile phones and new services. The area uses 10‑digit dialing for local calls, and phone numbers here follow the Eastern Time zone. You’ll see 857 on both business and personal lines across Boston’s busiest neighborhoods and campuses.
Major communities in the 857/617 overlay include:
This area code covers many of the region’s best-known landmarks, including Fenway Park, Boston Common, and Logan International Airport in East Boston. In Cambridge, it reaches world-class universities like Harvard University and MIT, which anchor a huge tech and research scene. These sites help explain why demand for phone numbers in and around Boston stays high. With an overlay, both 857 and 617 work in the same places, so the area code alone doesn’t pinpoint a specific neighborhood.
Area code 857 was introduced as Boston’s modern companion to 617 to prevent number exhaustion. Many long-time residents and businesses still use 617, while newer lines often receive 857, but both connect across the same calling area. The overlay means you can’t tell whether a number is mobile or landline just by the area code. This setup keeps Boston connected while preserving the historic 617 identity that locals know well.
"Year established: 2001" — North American Numbering Plan Administration (NANPA)