These days, even telephones are usually provided over the internet, so much so that traditional phone lines are rapidly becoming obsolete, with their abandonment being announced. The good news is that VOIP (Voice over Internet Protocol) calls are MUCH cheaper. The bad news is that you can't get power from the exchange - so, in case of a power cut, you'll need a UPS (uninterruptible power supply).
Most people take VOIP services from their internet provider, but that's not necessary. We used our first VOIP provider (WorldeXchange was also our first broadband provider), but they're now owned by Vodafone, so when we changed to fibre, we also changed our ISP. However, while we are very happy with the ISP services, we've changed our VOIP services to 2Talk. It's generally the cheapest (calls to England, USA, Australia and much of the world are the same as Auckland or Christchurch), and provides maximum user control (can be dangerous).
Mobile phones are a whole different ball game. There are only three main networks in NZ. For a long time, we stayed with Vodafone, but as more people called us, missed calls became an issue. We're only 2-3 km from Lower Hutt CBD - but the hills mean we are in a weak signal area. Spark, of course, is stronger, but we were surprised to see that at our house, 2Degrees is strongest. We have dual SIM phones, so we have our original number with The Warehouse mobile (using 2Degrees network) and the other on Skinny (budget service on Spark network). Note that both Skinny and The Warehouse use 28-day rather than monthly billing periods.
As a fan of open-source software, I find Jitsi Meet a great option. It's open-source and seems no worse than others and better than some, such as FB Messenger. Jitsi is open source, and although it comes in various versions (such as Android), it runs in a browser. After the URL, just add your meeting name, and you're away - no installation required. If you want to set up a meeting, just "start a new meeting" and let others know the name. We had a few initial issues - ad-blockers and giving our browser access to the camera and microphone, but that's the joys of living in a world of less than honest people.
One internet issue that we have found less than simple is speed. When we switched to fibre, we did get an increase, but for most of our use, it was not overly dramatic. This is hardly surprising - other factors such as processing on the host, and even the weather (mainly if we're using Wi-Fi) or school holidays can slow things down. But we've found factors that can make a difference.
Where one PC is normal and another is slow, something is slowing it down. We shut down our machines daily, so they should be fast at the start of each day. When one isn't (we now test our speeds every few months), it would be nice if it told you what the problem is - but there are so many permutations it's a question of working through them one by one. I suggest starting with testing a cabled network rather than Wi-Fi. Then make sure drivers are up to date. If the problem is due to some software, it's a question of testing with each one stopped. There are many other factors.
Alternatively, the whole system can be slow. Simply rebooting the router may clear that. These days, people are connected via fibre (and if you're not, and it's available, why not?) Restarting the router may not solve the problem. That's when restarting the ONT is called for.