I have two domains: comn.in, comn.us I would like to start a free domain registration service by using these domains. eg: www.userdomain.comn.in, www.userdomain.comn.us thoughts and ideas are appreciated.
wild card can only point to one server. Here each user will have different hosting servers. So each users domains have to be pointed to their servers dynamically on users request.
You are confusing domains and servers. A server can have many domains. You will need to "A" point each subdomain, if they are on different machines.
In case of huge domain creation request, its not practical to create separate records for each manually.