plain old telephone service vs. session initiation protocol POTS stands for Plain Old Telephone Service (business phone lines).  The acronym sounds like something hanging in your kitchen and definition makes people say, “Really, that’s what it stands for?”

SIP, on the other hand, stands for Session Initiation Protocol.  Nothing old fashioned about that.

Business people are starting to take notice of SIP and are asking about it more.  They’re wondering if it’s something they should be using.

Here’s a comparison between the two services: 

POTS lines are static.  If you have a POTS line in place, it uses the same capacity whether zero or a hundred calls are made or received on the line.

SIP trunks are dynamic.  They only exist when a call is taking place.  Afterwards, the resources (bandwidth) needed to place a call are freed up for other uses.

Phone calls on a POTS line are transmitted over the Public Switched Telephone Network (PSTN).  That’s the traditional phone company network, using copper phone lines and phone company switching equipment.

SIP calls are transmitted over the internet.  SIP is Voice over IP (VoIP).  SIP calls might terminate on the PSTN but they always originate on the internet or a data network.

A POTS line requires a twisted copper pair.  If you order a new POTS line, a local phone company, like Verizon, AT&T or CenturyLink, is involved.  They determine if there is a line available and then create or add it to an account, assign a phone number and a technician is dispatched to test and tag it at the point of demarcation.  From that point, you may need additional inside wiring or your telephone vendor to complete a cross connect from the demarc to your phone equipment.

A SIP trunk requires internet bandwidth.  It exists through programming; virtually no physical work is needed to activate a SIP trunk.

A POTS line requires a few days to activate.  Mostly the installation date is determined by the availability on a technician’s schedule.  If there are no existing copper pairs available, however, installation could take weeks.

If a company account already exists, a SIP trunk could be established in hours.   

A POTS line has its own power supply.  If your company experiences a power outage and your using POTS lines, you should still be able to make and receive calls.

SIP requires an internet connection, so if your power is out, and there’s no battery backup, you won’t be able to place a call.

With POTS, an emergency service professional will be able to pinpoint your location if you call 911 and can’t speak.

SIP requires your company to provide location information to your service provider and that information must be delivered to emergency services.  But with VoIP, it’s possible to take a desk phone and connect it to a different internet connection and still place and receive calls.  If someone does that and needs to reach emergency services but can’t communicate, emergency personnel could be dispatched to the wrong location.

The ratio of phone numbers to phone lines is one to one with POTS.  It’s possible to have other numbers forward to a particular POTS line phone number, but it’s not possible to have a group of POTS lines share a pool of phone numbers.

A group of SIP trunks could share a pool of phone numbers.  This provides more flexibility and makes better use of resources.

POTS phone numbers are location specific.  The location where they exist determines the area code and prefix.

SIP trunks can use a phone number from any location.  You could assign a Los Angeles phone number to a SIP trunk located in New York City, for instance.  This allows a company to consolidate their phone numbers at a central location, to experience economies of scale, or make calls appear “local” when they are actually originating from a distant location.

POTS or business phone lines range in cost from 20 to 50 dollars per month.

SIP trunks are typically less than $20 per month, per trunk or voice path.

With the development of VoIP, traditional phone services, like POTS, are being phased out.  POTS lines are still used for alarm, fax and elevator lines, where dependability, a power supply and compatibility are key.  Also, a few POTS lines and DSL or cable is the most cost effective phone and internet solution for smaller businesses and branch offices.

If you’re uncertain whether POTS or SIP is a better fit for your organization, contact CarrierBid today for a free consultation.


Related Posts:

Call us at


for immediate service or fill out the
form and we’ll be in touch right away.

  • Please describe how we can help:
    What services are you considering to drive your business higher?
    What challenges are you currently facing?