We use 4G for our home broadband service. It's faster than ADSL and VDSL here.
However we use a modem/router dedicated to the task which lives on a window sill upstairs connected to an antenna on the roof which helps reduce latency and improve upstream speeds (in particular).
It has VOIP capability and also ethernet ports, and so powers the home network just like any other always-on connection and provides the "landline" using a SIP VOIP account. The idea of having a physical wire coming to the house seems odd now.
I wouldn't try doing this with a mobile phone. It gets hot. It would have to be permanently on power. It may well crash. It has tiny antennae, even without the one on the roof, the modem has good antennae and still manages decent speeds. Also, a lot of plans which are said to be unlimited won't be so if you use it as a "hot spot" (share the connection) or may throttle the speed once you've used a certain amount.
We normally see 20 to 40 Mbps down and 45 to 50 Mbps upstream with our 4G setup.
This is in the UK, in a rural area, on an EE data plan which gives us 100GB/mo.
Streams HD TV perfectly, does VOIP, all good.
The plan comes with a modem however we use our own - google Huawei B593.