I just found this on the BubHub site, might be of some help
Travelling in taxis
A child under the age of 7 is safest when travelling in a capsule or child restraint correct for it's age/size. Where possible, it is best if you can supply your own car seat when intending to travel in a taxi to ensure that your child is safe along with being more cost effective. All taxis should have the correct anchor point for fitting the restraint, but it is always advisable to call the taxi company in advance to check.
Taxi companies may be able to provide child restraints if they are given sufficient notice. A surcharge is the norm for the hire of the child seat and you will often have to pay for the taxi to collect the seat from a depot or taxi company's headquarters. Your journey will be metered from the carseat collection point, to wherever you are picked up and then onto your final destination. Check all charges with your taxi company in advance and ensure that you book your vehicle well in advance (at least an hour).
Older children (up to age 7 years) must use a child restraint if one is available. If there isn't one available, the child must wear a properly fastened and adjusted seatbelt.
The rules for travelling in taxis with very young children do vary from state to state within Australia. It is advisable to check with taxi companies when booking and to order a child seat in advance. Customer service desks at airports (both within Australia and internationally) should be able to assist you with booking taxis with childseats if you are not able to pre-book a taxi prior to your arrival.