North American Numbers Source-cited · ownership disclosed
Area code
857
In service
United States · since 2001

Boston (overlay)

Area code 857 is an overlay of 617, serving Boston and its inner-ring communities. It shares its geography with 617 and requires ten-digit dialing.

The essentials Numbering data · NumberResearch · as of 2026-09-18
Place
Boston (overlay)
Type
geographic
Status
in service
In service since
2001
Projected exhaust
2066 Q3

Status, dates and counts are read from NumberResearch (NANPA / CNAC / FCC records). Assignment records show initial assignees, not the carrier serving a number today.

A · Where it is

Where 857 is

Inner-ring Greater Boston within Suffolk, Middlesex, Norfolk, and Essex counties..

Communities served wholly or partly by 857:

BostonCambridgeBrooklineNewtonQuincySomervilleChelsea

Same service area as 617; the two codes are geographically identical.

B · Relationships

How it relates to other codes

The codes 857 was split from, spawned, or shares its area with. A split divides the map and changes some numbers; an overlay shares the same ground and changes none — what's the difference?

Overlay · 2001 617 Boston 857 overlays 617 across the same territory.
What's changing. Overlay of 617; ten-digit dialing mandatory since 2001. Per Wikipedia, 617/857 projected to exhaust by 2059.
C · History

How 857 got here

2001-05-02
Area code 857 overlaid onto 617; ten-digit dialing mandatory.
Source: Wikipedia
D · Capacity

How full it is

Prefixes assigned
382
Prefixes available
418
Thousands-blocks assigned
3,234

Prefix-assignment counts describe allocation to carriers, not how many individual numbers are in use. Full technical records: NumberResearch ↗.

Compare 857 with another code →
Sources
Wikipedia ↗
Area code 857
NumberResearch.org ↗
Live status, dates, assignment counts and exhaust forecast — data as of 2026-09-18 (CC BY 4.0).

Place, relationships and history above are compiled by North American Numbers from the sources listed and last checked 2026-09-18. A check date is not an expert review — see how this is made. Flag an error.