There are many VLANs in my account which don't have billing items, which means they are not explicitly purchased. Therefore, I can't choose them as my destination VLANs if I want to create an autoscale group and deploy the VMs across more than two such VLANs. So how these non-purchased VLANs end up existing in my account? Is it because I created autoscale group early without specifying the VLAN, and that SoftLayer automatically and randomly chose one for me?
These kind of vlans (which don't have billing items), are assigned to your account at the moment to order a server, vyatta, etc.
For example, If you wish to order a server in "Dallas 5", we assume that you don't have any vlan in that datacenter, SoftLayer will provide a vlan for that server. This is the case when this kind of vlan is assigned to your account.