Guide to IP telephony
IP telephony & VoIP — how it works
VoIP means calling over the internet instead of the copper network. Here is how it works, what you need, and how IP telephony differs for the home and for business.
What is IP telephony?
IP telephony — also called VoIP (Voice over IP) — means phone calls travel over the internet instead of the old telephone network (PSTN). Your voice is turned into digital data packets, sent over your broadband using the SIP protocol, and reassembled into audio at the other end. The result is the same call as before, but cheaper, more flexible and with more features.
Because the call is just data, it does not matter where you are — the number follows you wherever you connect, at home, at the office or on your mobile.
What you need
IP telephony for home and for business
At home
A simple IP telephony subscription gives you a phone number, cheap calls and the option to keep your old number. Call from an IP phone, your ordinary phone via an adapter, or an app on your mobile.
Business
Businesses connect their phone system (PBX, e.g. 3CX) to the phone network with a SIP trunk — multiple simultaneous channels, your company numbers, voicemail, queues and IVR. Scale up and down as needed without new hardware.
Traditional landline vs IP telephony
Want to get started with IP telephony?
Internetport offers IP telephony for individuals and SIP trunks for businesses — Swedish support, keep your number and pay only for what you call.
Common questions about IP telephony
What is VoIP / IP telephony?
VoIP (Voice over IP) means making phone calls over the internet instead of the traditional copper phone network. Your voice is turned into digital data packets and sent over your broadband using the SIP protocol. IP telephony is the same thing — telephony delivered over an IP network rather than the old PSTN line.
What do I need to use IP telephony?
Three things: a broadband connection, a SIP account from an IP telephony provider, and a device to call with — an IP phone, an ATA adapter that connects your existing phone, or a softphone app on your mobile or computer. No new cabling is needed; it runs over the internet you already have.
Can I keep my old phone number?
Yes. In almost all cases your existing landline or mobile number can be ported (moved) to IP telephony, so you keep the same number when you switch. You can then use it from anywhere with an internet connection.
How much internet speed does a VoIP call need?
Very little — roughly 0.1 Mbit/s (100 kbit/s) per call, so any normal broadband handles many calls at once. What matters most is a stable connection with low latency and jitter; that is what keeps call quality clear.
Does VoIP work during a power or internet outage, and can I call 112?
Because VoIP runs over the internet, it needs power and a working connection — during an outage a mobile phone is the backup. Emergency calls to 112 do work over IP telephony, but the location is not always sent automatically as it is from a fixed landline, so always state where you are. For businesses, a mobile or 4G/5G failover keeps you reachable if the fibre goes down.
What is the difference between IP telephony and a SIP trunk?
IP telephony is the general term for calling over the internet. A SIP trunk is the business version: a connection that links your own phone system (PBX/switchboard, e.g. 3CX) to the phone network over IP, with several simultaneous channels and your company numbers. Home users typically use a plain IP telephony subscription; companies with a switchboard use a SIP trunk.