I have just read Rod Perry's article regarding the postcard with the Miller & Sons label and would like to offer the folllowing comments:
1) there is no record of the hand stamp "canceling" the label on the card (pictured above) being in use at the GPO (which was only two blocks away from Miller's Pharmacy and in the same street) or at any other Hobart post office.
Therefore, I think it is unwise to declare that this card is commercially used in the sense that it has been received by and delivered to the addressee using the services of the P.M.G. Dept.
If it can be ascertained that Miller & Sons ran their own local courier service using these labels to denote prepayment for carriage, I guess that one could then say that the card has been commercially used but there is no primary evidence that I can find indicating that such a service existed in 1906 or at any other time for that matter.
I also think that it is unwise to assume that the example with "1/3" written in pen denotes that a delivery cost of 1/3d has been charged by Miller & Sons for the delivery of some goods.
I am of the opinion that this item was not delivered by the post office nor by a messenger working for a local post service but was produced "just for fun".
Re point 1. I don't think Rod was ever implying that it was used in the 'official postal system' He states it is a cinderella and commercial use would apply to it's use as a cinderella similar to the Cycle Mails or Boyd's Messenger Service.
The card was written late at night long after the post had closed. The writer may have wanted it delivered post haste.
1/3d is not out of the realms of possibility for messenger deliveries, just look at the cycle mails. 1 Shilling and 2/6 for the first issue.
Many Chemists delivered drugs, medicines and orders. My first part time job was at Peppin's Pharmacy in Footscray and part of the job was to deliver prescriptions by bicycle. (Should have made my own bicycle courier stamps)
Millers seems a quite large establishment and it wouldn't surprise me at all to find they created a delivery service as a side line to their pharmaceutical deliveries.
This all happened over 100 years ago and I don't think we will ever know for sure unless records from Millers surface proving the existence of their messenger service.
I still think it is a distinct possibility that there was one.
New discoveries are being made every day and more recent items than these are being discovered.