Quick answer: Co-existence can affect internet speeds on FTTN, FTTB or FTTC services due to the interference of different types of DSL technology applied to the same copper cable.
This means your maximum available line speed during the co-existence period will likely be closer to the slower end of the maximum available speed range provided by the NBN Co.
For example, if your maximum available speed on your nbn™ FTTN or FTTB is between 33 Mbps and 82 Mbps and your home is subject to Co-existence, your maximum available speed will be closer to 33 Mbps. After Co-existence ceases to apply to your address, your maximum available speed will be closer to 82 Mbps.
When will co-existence cease to apply?
Co-existence will cease to apply when all ADSL connections have transferred over to the nbn™ access network which should be no later than 18 months after the nbn™ was first available in your area. At this time, you should be able to attain speeds closer to the higher maximum available speed.