Area codes / Tennessee / 423
The 423 area code
423 is an area code in Tennessee, in the Eastern and Central time zones. Get a local 423 number for your business, shared by everyone who answers it, or bring the 423 number you already have.
423 at a glance
Get a 423 business number
When you sign up for Onyx Phone, you pick a local number by area code: search 423, narrow it by the next three digits or the last four if you want something memorable, and it's yours on the spot. Which numbers are free changes daily. If you don't find one you like, 729 covers the same area.
The number rings everyone you assign to it, in the browser, on the iPhone and Android apps, and on desk phones, and texts from it are unlimited once US carriers approve your business. Your plan includes one number for each user, and more numbers are $5 a month.
Calling 423 customers
Local calls in 423 are dialed with all ten digits: the area code, then the number. 423 spans the Eastern and Central time zones, so the local time depends on where the caller is.
Calls from Onyx Phone show your business number, and once your business is verified, your caller ID name too, so 423 customers see who's calling.
Questions about area code 423
What state is area code 423?
Area code 423 is in Tennessee.
What time zone is area code 423 in?
Area code 423 covers places in the Eastern and Central time zones, so check which one a caller is in before you call early or late.
Is 423 an overlay area code?
Yes. 423 shares its area with 729. Numbers in either code ring the same region, and local calls there are dialed with all ten digits.
Can I get a 423 business number?
Onyx Phone sells US local numbers. When you pick your number, search the 423 area code; which numbers are free changes daily. If none are free, 729 covers the same area.
Can I keep the 423 number I already have?
Yes. Moving a number to Onyx Phone is free on every plan and usually takes 3 to 7 business days. You answer on a temporary number until it moves.
Included on every plan
Starter is $17, Business is $29, Scale is $42 per user a month, or less billed yearly. The plan includes a business number for each user and unlimited calling and texting in the US and Canada. Every plan starts with a 7-day free trial, and moving your current number over is free.
Area code data from the North American Numbering Plan Administrator (NANPA), file of October 24, 2026.