SolusVM is great for managing virtual private servers. It also has great integration into many of the billing solutions used such and WHMCS. But like others have stated if you are looking to sell virtual hosting accounts then it would not be a choice. We use WHMCS/cPanel for all of our shared hosting accounts. Other choices are available. Even some free alternatives to cPanel exists such as zPanel. However I am not aware of integrations into billing solutions.