Competition in infrastructure (which a telecommunications network is) is inherently more expensive. This is because you end up with more bureaucracy and more physical plant/capital. You also end up with a less efficient network (a few years ago if you were with a T/C ISP then a connection from Auckland to Wellington went via Australia due to an interconnect disagreement) with less coverage as each of the competing networks only rolls out to those areas where they're likely to make a profit and, in regards to mobile, they're the same areas. Land based networks are unlikely to get competition at all as each competitor reduces income and that cabling and plant is expensive. Basically, competition in a land based network is a bad business decision which is why Telecom is, essentially, still a monopoly.
Due to these limitations we (the taxpayers) are now having to pay out billions of dollars of subsidy to private profits to upgrade the land based network that, if it had been left as state owned, would already have had those billions spent on it from the profits. We would also have had better mobile coverage as, instead of spending twice as much or more to cover the same areas, we would have spent that money to cover more area instead.
Competition: Expensive and inefficient.