I was still able to access Optus 3G in Southport, TAS, this past weekend. Why is that? I noticed that I had 3G coverage, followed by H+ (which is also a 3G service). Is it possible that Optus hasn’t yet phased out 3G in certain rural locations? Are there any other areas where this might be the case?

It’s quite possible that Optus hasn’t completely phased out 3G coverage in certain rural areas like Southport, TAS. In many cases, telco companies have opted to maintain 3G services in less populated regions to ensure that residents and visitors still have access to mobile connectivity, especially where 4G or 5G networks may not be fully deployed or reliable.
The presence of H+ indicates that you’re accessing the higher speed version of 3G, which can still be useful for basic internet needs. There may be other rural or remote areas across Australia where 3G remains, primarily due to these reasons. If you’re interested in finding out about specific areas with 3G coverage, checking Optus’ coverage maps or contacting their customer service could provide more detailed information on their network status in different regions.