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

Knowing whether you have a VoIP phone line or not is a very 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 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 cell phone / smartphone can, however, be used to send and receive faxes).

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

If your phone is connected to an ethernet cord, then it is definitely a VoIP phone.

If your phone is connected to a traditional phone cord, then it could be either a VoIP or traditional 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 certainly 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 a traditional line.

Step 4 – contact your phone provider

Is your phone provider’s line a traditional telephone line, a cable/internet line with phone running over it, or a VoIP line?

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

If it is a VoIP provider, you certainly have a VoIP phone line. Most VoIP providers will have a small box to plug a phone into that also connects to the internet.

Most cable/internet providers provide a “landline” service, however the underlying technology is VoIP. If you have a cable/internet provider for your phone line, it is probably (but not certainly) a VoIP phone line.

Many traditional telephone providers provide analog/traditional phone lines, however many of them are replacing their traditional phone lines with VoIP technology. If you have a traditional telephone provider for your phone line, it is probably (but not certainly) 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 certainly 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 taken 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 would 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 in our experience this is no guarantee of either a VoIP or traditional phone line.