The 443 area code overlays the eastern half of Maryland — Baltimore and its suburbs, Annapolis, and the entire Eastern Shore down to Salisbury and Ocean City — on exactly the same footprint as 410, with 667 stacked over both. In service since June 1, 1997, it exists to add numbers to that territory without changing a single one that was already ringing.
A code born without borders
Every area code before the overlay era earned its own patch of map. 443 never got one. When Bell Atlantic Maryland reported that the eastern half of the state was burning through numbers, the Maryland Public Service Commission approved a general-purpose overlay rather than another split, and NANPA assigned 443 to sit directly on top of 410 — notice went to the industry in Bellcore letter IL-96-06-008 on June 21, 1996.
That letter spells out the bargain. The two codes would share identical boundaries — the Baltimore and Salisbury LATAs, harbor to beach — and no existing 410 number would change. The region had earned its caution: the 1991 split that carved 410 out of 301 had just renumbered half of Maryland, and nobody wanted to repaint the truck twice in one decade.
Switched on empty, on purpose
443 went live on June 1, 1997, and then did something no split code ever does: nothing. The 1996 letter held its prefixes in reserve until two conditions were met — mandatory ten-digit dialing in force, and every assignable prefix in the 410 pool handed out. So the new code idled through its first months with no subscribers at all, a full warehouse behind a locked door, and assignments could only begin once 410 finally ran dry — an exhaust Bell Atlantic was forecasting for the end of 1997.
The design outlived its era. The Hudson Valley’s 329 and the Florida Panhandle’s 448 both launched under the same condition decades later — sealed until their parent codes empty.
Ten digits before the first subscriber
Making one map hold two codes meant retiring seven-digit dialing, and Maryland did it statewide and early: ten-digit local dialing was permitted from May 1, 1996 and mandatory from May 1, 1997 — a month before 443 switched on. Marylanders spent that spring dialing ten digits for a code that did not yet have a single customer. A companion Bellcore letter ran the identical playbook in the western half of the state, where 240 overlaid 301 the same June morning.
The early conversion still pays. When the 988 crisis line forced 82 seven-digit area codes onto ten-digit dialing in 2021, NANPA Planning Letter PL-556 listed the converts state by state — and Maryland appears nowhere. The question the rest of the country faced in 2021 was settled here in 1997.
Full by December 2001 — a forecast that missed by a decade
Everyone expected 443 to fill fast. On January 3, 2001, the Maryland PSC approved a third code for the territory in Case No. 8853, Order No. 76681, and NANPA Planning Letter PL-266 of March 14, 2001 laid out the plan: 667 would switch on the day the combined 410/443 pool exhausted, a date then anticipated to be December 1, 2001.
That day kept not coming. Conservation measures and cooling demand for new lines appear to have stretched the pool far past the forecast, and for eleven years 667 remained a paper code — assigned, never activated. NANPA reissued the plan as Planning Letter PL-427 on October 10, 2011, setting activation for March 24, 2012 — and noted that no permissive dialing period was needed, because eastern Maryland had already been dialing ten digits since 1997.
Where the three-code stack stands in 2026
The pattern is holding. NANPA’s April 2026 NPA Exhaust Analysis, built on numbering data as of March 1, 2026, projects the 410/443/667 complex to exhaust in the first quarter of 2036 — nudged later from the second quarter of 2035 in the prior forecast. The deadline has been receding from 443 its whole life. Whenever it finally arrives, relief would follow the template this code helped write: another overlay on the same map, with nobody renumbered.
What a 443 says on a Baltimore caller ID
Two things, and only one of them is spoken. The unspoken one is vintage: no 443 number can predate the code’s 1997 launch, so the code skews toward mobiles, VoIP lines, and younger companies, while a 410 might have answered the same digits since the Schaefer administration. The spoken one is locality — same rate centers, same cost to call, same standing as 410 and 667, and the same answer-rate advantage a local display earns with Baltimore, Annapolis, and Shore customers. Just remember the display is a claim: spoofed caller ID borrows local digits precisely because they get picked up.
SIPNEX stocks eastern-Maryland numbers the way the network actually organizes them — DID inventory by rate center, 443 and its 410/667 siblings alike — and feeds them over SIP trunking into whichever switch answers your calls. We operate under a direct FCC carrier license, hold registration in the Robocall Mitigation Database, and sign outbound traffic at A-level attestation on our own STIR/SHAKEN certificate; toll-free numbering runs under our RespOrg registration.
Quick answers on 443
What cities does the 443 area code serve?
Baltimore and its orbit — Towson, Dundalk, Glen Burnie, Columbia, Ellicott City — plus Annapolis on the western shore, and the whole Eastern Shore across the Bay: Chestertown, Easton, Cambridge, Salisbury, and Ocean City. The footprint is identical to 410 and 667, because 443 is an overlay: it shares every boundary rather than owning territory of its own.
When did the 443 area code go into service?
June 1, 1997, per Bellcore letter IL-96-06-008 — but it launched deliberately empty. Its prefixes were held back until every assignable 410 prefix was gone, so working 443 numbers only appeared once the old pool ran out — an exhaust Bell Atlantic projected for the end of 1997. Ten-digit local dialing had already been mandatory across Maryland since May 1, 1997, in preparation.
Is a 443 number newer than a 410 number?
As a rule of thumb, yes. 410 numbers have been issued since 1991 — and inherited lines reach back through 301 to 1947 — while no 443 number can predate the code’s 1997 debut. That makes 443 read as the newer-vintage code, common on mobiles and VoIP lines. Functionally the two are interchangeable: same territory, same rate centers, same cost to call.
Do calls to 443 numbers cost more than calls to 410 numbers?
No. An overlay changes nothing about rating or routing — a 443 number is billed exactly like a 410 or 667 number from the same rate center. The only cost the overlay imposed was a dialing habit: with multiple codes on one map, every local call has needed all ten digits since 1997.
Will the 443 area code run out of numbers soon?
Not soon. NANPA’s April 2026 NPA Exhaust Analysis shows the combined 410/443/667 pool lasting until the first quarter of 2036, and that date moved later — from mid-2035 — in the most recent forecast cycle. When exhaust does approach, the established fix is another overlay on the same footprint, so existing 443 numbers would not change.
If your customers are in Baltimore, Annapolis, or out on the Shore, SIPNEX can put 443, 410, or 667 digits on your outbound display from live rate-center inventory — FCC-licensed, A-level signed, dialer-ready over SIP. Baltimore digits are a short order: look over rates, put questions to the carrier team, or ring (833) 665-2220.
Keep reading.
The carrier built by operators, for operators.
FCC-licensed carrier with its own STIR/SHAKEN SP certificate. Operator-owned. SIP trunks built for operators who dial at volume.