According to one VPN manufacturer, iOS does not support split-tunneling on Apple devices. All traffic must be passed through VPN end-point.
Snipet taken from online support: http://www.watchguard.com/help/docs/wsm/11_XTM/en-US/index.html#en-US/mvpn/ipsec /mvpn_ipsec_ios_vpn_c.html
Select Yes, force all Internet traffic to flow through the tunnel..
This configures the tunnel for default-route VPN. The VPN client on the Mac OS X or iOS device does not support split tunneling.