Area codes / Colorado / 303
The 303 area code
303 is one of the original 1947 area codes in Colorado, in the Mountain time zone. Get a local 303 number for your business, shared by everyone who answers it, or bring the 303 number you already have.
303 at a glance
- State
- Colorado
- Time zone
- Mountain
- In service since
- 1947
- Local calls
- Dialed with all ten digits (area code and number)
Get a 303 business number
When you sign up for Onyx Phone, you pick a local number by area code: search 303, 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, 720 and 983 cover 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 303 customers
Local calls in 303 are dialed with all ten digits: the area code, then the number. Callers are on Mountain time, so set your business hours to match if most of your customers are here.
Calls from Onyx Phone show your business number, and once your business is verified, your caller ID name too, so 303 customers see who's calling.
Questions about area code 303
What state is area code 303?
Area code 303 is in Colorado.
What time zone is area code 303 in?
Area code 303 is in the Mountain time zone.
Is 303 an overlay area code?
Yes. 303 shares its area with 720 and 983. Numbers in any of these codes ring the same region, and local calls there are dialed with all ten digits.
Can I get a 303 business number?
Onyx Phone sells US local numbers. When you pick your number, search the 303 area code; which numbers are free changes daily. If none are free, 720 and 983 cover the same area.
Can I keep the 303 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.