Cant connect from Mobile Device

We have the following set up:

Windows Mobile Device with GPRS connection (win empedded handheld 6.5 Prof)
Windows Server PC with SQL Server 2012
VPN Network where both devices contained (the cell carrier routes certain IPs inside VPN)

Status:

With the above set up I can ping directly from the mobile device to Windows server internal IP via GPRS.

Question:

Can I create connection to SQL server from my Mobile using the server's internal IP?
I am using the following con string with no luck:

"Data Source =xxxxxxxx,1433;Initial Catalog=xxxxx;Integrated Security=SSPI;User id=xxxxx;Password=xxxxx;Connect Timeout=15";