Android and IPhone App Develop

I have Windows Server 2012 functions as VPN Server All of my clients uses PPTP, L2TP, SSTP protocols to connect to my server and surf internet using my VPN. I need Mobile Application to simplify the creation of user name and password for any new customer from mobile, and simplify the creation of VPN connection. the most important thing in this application is to connect to internet using SSTP protocol from mobile can you do that? what is the estimated cost and time? thanks in advance