How do I know if I have a VoIP line or traditional POTS line?

LAST UPDATE: March 6th, 2018

Knowing whether you have a VoIP phone line or not is a difficult question.

VoIP has become a part of many parts of the phone network. In some cases, even when all phone lines in a building are traditional (analog) phone lines, the connections from the building to the phone network (or parts of the phone network) may be using VoIP to transition a call. As well, it is impossible to know what type of telephone line technology is at the opposite end of a call.

Why would anyone want a traditional (analog/POTS) phone line?

One of the most common questions we receive is how to send a fax over a VoIP phone line. It’s also one of the most difficult ones to answer (it’s almost impossible to get a VoIP line to a level of guaranteed service for fax).

VoIP is known to scramble fax signals so that the service becomes unreliable. In some cases, faxes are transmitted, in others they are not.

Step 1 – is your phone a cellular (mobile) phone?

If your phone is a cellular (mobile) phone, you do not have a traditional phone line or a VoIP phone line; you have a cellular phone line.

Fax cannot operate over a cellular phone line (a smartphone can, however, be used to send and receive faxes).

If you call with your smartphone over an app other than the regular phone app on your phone, then you might be accessing a VoIP phone service via your smartphone.

Step 2 – is your phone connected to a traditional phone cord (RJ-11) or an ethernet cord (RJ-45)?

If your phone connects to an ethernet cord, then it is most likely a VoIP phone.

If your phone connects to a traditional phone cord, then it could be either a VoIP or traditional (analog/POTS) phone system.

Step 3- is there an ATA box or ATA analog phone adapter somewhere on the line?

If there is an ATA box or analog phone adapter somewhere along the phone line, the line is a VoIP phone line. ATA phone adapters are used to adapt a traditional telephone to a VoIP phone network.

If there is no ATA box or analog phone adapter, the line may be VoIP or POTS.

Step 4 – does your phone line go out during a power outage?

A phone line that does not go out during a power outage points to a traditional POTS line. It could, however, be a VoIP line with a battery backup on the system.

Step 5 – is your phone offered by a cable provider or a phone provider?

A phone offered by a traditional cable provider points to a VoIP phone line. A phone provided by a conventional phone provider suggests a regular phone line.

Things are changing in this area – AT&T U-verse and Verizon FiOS phone systems are both VoIP phone services provided by a traditional phone company.

Contact your phone provider to ask if your phone line is a VoIP line or a traditional analog phone line.

Does having a dial tone signify if the phone line is VoIP or a traditional line?

No. A phone system without a dial tone is a VoIP phone system, but one with a dial tone could be either type.

Many VoIP phone systems will have a dial tone when the phone is off the hook.

Is there a database of phone numbers that are VoIP or regular lines?

Not that we’re aware of.

Tropo (part of Cisco) has listed a method of querying the Whitepages Pro API to see if a number is a VoIP, cellular, or traditional phone line.  We have not tried this approach.

The challenge with database driven queries is that they are not guaranteed to be correct. With number portability, a phone number can change from a mobile to a landline (or vice versa), and the database is not aware of the change. A phone provider may have a mix of VoIP and traditional phone numbers, and they may be intermixed. As well, a phone line may be “traditional” up to the building, but inside the building use VoIP technology to manage internal calling.

Is there a way to measure a line’s current or voltage to tell if it is a VoIP or traditional phone line?

Not that we’re aware of.

Many VoIP phone systems are only VoIP up until the line reaches the building. Once in the building, they use the traditional phone lines already in the building. If this is the case, a “traditional” phone line may register the same current or voltage as the phone system is emulating the traditional phone signal.

Is there a way to tell by the call quality of the line?

Not that we’re aware of.

We’ve seen some conversations that mention that a VoIP phone line will have delays or echoes. However, this is no guarantee of either a VoIP or traditional phone line.

Sources and more resources

Fax AuthorityHow to fax with a VoIP phone line (such as Google Voice, Skype, Magic Jack, and more) – our guide to using fax with a VoIP phone.

Consumers UnionHow Can You Tell if You Have a VoIP Home Phone Service? – Some ideas on how to tell if you have a VoIP phone number or a regular analog phone number.

SpiceworksOdd Troubleshooting question… VOIP vs POTS lines – A forum discussion on how to figure out whether a phone line is a regular (POTS) or VoIP phone line.

TropoDetermining a phone line type (cellular, landline, or VOIP) – A method for programmatically determining a phone number type from a database.

DSL ReportsHow can I tell if someone has VOIP? – A forum discussion on how to tell what type of phone system somebody else is running.

QuoraHow can you programmatically determine if a phone number is VoIP, prepaid mobile, mobile, or fixed line? – Some ideas on how to programmatically find out the type of phone line a phone number is.