This is a genuinely common question, and the honest answer is: it depends entirely on the specific provider, not on any general rule.
Why this varies so much
Some virtual address providers allow an additional, unrelated business to use the same address at no extra cost. Others charge a fee per additional business, and some don't permit it at all under their standard terms [Virtual Address, virtualaddress.com.au]. There is no industry-wide standard here, which is exactly why this needs checking directly rather than assumed.
Why it matters more than it sounds
If you run two genuinely separate ventures, perhaps a sole trader ABN for one and a company for another, you might reasonably expect one subscription to cover both. If your provider's terms don't allow this, you could end up needing two separate address subscriptions, doubling a cost you assumed was already covered.
What to actually ask before assuming
Before relying on one virtual address for more than one business, ask the provider directly: does this plan cover multiple entities, is there an additional fee, and does each entity need its own registration on file with them.
Where Space Penguin fits
Confirm directly with Space Penguin whether your specific situation, multiple ABNs, multiple companies, or a mix of structures, is covered under one subscription before assuming it is. Space Penguin offers virtual addresses in Sydney and Melbourne from $20 per month plus GST. Visit spacepenguin.io/virtual-address for current details.