If you void an invoice, it's treated as if it doesn't exist. So then, if you have a pending service, or a suspended service that is attached to that invoice, the pending service will be created, and the suspended service will be unsuspended. If you are voiding invoices, you should be aware of this and take any necessary action on the service first.
If you manually suspend a service as an admin, it won't be unsuspended except by an admin.