If you would like to limit a subset of users to only call Australian numbers, the following voice routing policy and PSTN usages.
Please replace XXXXXXXXXX with your Teams Direct Route subscription id (ie 21xxxxxxxxx)
Set-CsOnlinePstnUsage -Identity Global -Usage @{Add="MyCloudVoIP-PSTNUsage-AU-Restricted"}
New-CSOnlineVoiceRoutingPolicy "MyCloudVoIP-VRP-AU-Restricted" -OnlinePstnUsages "MyCloudVoIP-PSTNUsage-AU-Restricted" -Description "Allows calls to Australia Only"
New-CsOnlineVoiceRoute -Identity "MyCloudVoIP AU Restricted Primary" -NumberPattern "^\+?61\d+$" -OnlinePstnGatewayList XXXXXXXXXX.tdr.mycloudvoip.com.au -Priority 1 -OnlinePstnUsages "MyCloudVoIP-PSTNUsage-AU-Restricted"
New-CsOnlineVoiceRoute -Identity "MyCloudVoIP AU Restricted Secondary" -NumberPattern "^\+?61\d+$" -OnlinePstnGatewayList XXXXXXXXXX.tdr-b.mycloudvoip.com.au -Priority 2 -OnlinePstnUsages "MyCloudVoIP-PSTNUsage-AU-Restricted"
Apply the new Voice Routing Policy – MyCloudVoIP-VRP-AU-Restricted, to users you wish to restrict to Australian calls.