Suggestions for creating site-to-site vpn over 3g without using dyndns. note that now isp's are using their local ip ,it is not possible to use dyndns, what do you think?

Get public ip /static ip from your mobile ISP for a premium, at-least for one end. Then you can use OpenVPN to bridge your networks

can you explain more

you can use No-ip to create domain

www.noip.com