Here's my usage while in Taipei and Kaohsiung:
Got ChungHwa at T1 Arrival(Upon clearance exit --> Turn right head straight for Telecommunications Services, Long queue for Taiwan Mobile counter
). Asked for Passport and Singapore IC documents for processing(cannot siam), paid NT$500 - NT$150 global talktime using 019(Sounds like SingTel v019), -NT$50 card balance, Unlimited Data usage for 7days.
Plugged SIM into handset, SIM was activated(Activation text message received) and to check balance : *101*1
#Call(Remember to include #). Remember to change your language to English by following the language setup on the Prepaid Pack reference guide.
Turned on WiFi Hotspot function of my DUAL SIM fone while on-board HSR, able to retrieve emails from Tablet and prepare Hotel Check-in itineraries and directions from MRT exit.
Reception was crystal clear for calls, SMSes back to SG as well as locally.
1) I made a couple of local calls for confirmation of my itineraries as well as letting my mum call back SG relatives in the comfort of my Hotel room after a day's travelling from Plane --> HSR --> Metro -- > Walk to Hotel with Hardcase luggage. Everyone's playing on their fones while on the trains so much like back here. We're certainly not outstanding in this aspect.
2) Managed to contact my guide while on a day tour when the tourist group swelled up in numbers especially in rainy Jiufen.
3) Managed to SMS my SIS in Departure Hall T2 when her counter hadn't opened yet while i was done with my own check-in at Departure Hall T1. Minimised on her international SMS charges $$$.
Hope my usage will help give an idea on easing the communications part of your trip and not to stress out if you can't reach someone locally.