Though one of the most important, providing hiring inhouse 24/7 Sales/Billing support wont be as cost effective as hiring an offshore staff for the purpose.
The sales/billing operator we provide you have high commandment on English language and often knows a second languages as well (German/French/Spanish - depends on availabily).
They have hands on experience and right expertise in handling various billing softwares such as WHMCS, ModernBill, PerlBill, ClientExec, AWBS, Plesk HSPC and so on. Billing personnel in most cases has got good soft skills as well and has proven skills in converting an enquiry to an order. You get two in one, but no compromising quality on either!