Cellular Apple Watch Ultra 1 and cellular SE (new) not allowing SMS or iMessage when not in presence of iphone

Hi, my wife and I both have cellular enabled Apple Watches with an Optus Number Share each. We both can make calls when out and about on the watches without our iPhones, but they both will not work for text messages - either SMS or iMessage... tried resetting / re-pairing to now avail. Any ideas?