I have two 880 routers on 3G link and i want to create IPSec Site-Site VPN between the two points.
Is is it possible as 3G links on both the end donot have any static IP.
You would need to set up a tunnel between the points, and for that you need the IP addresses. Normally this would be done with fixed addresses, but it may be possible using the hostname of the remote node, if that is fixed. If the name is based on the IP address, which is not unusual, you'd need to contact your provider for a fixed IP address.
It is also possible the provider has disabled intermobile traffic, in that case they cannot directly communicate if in the same APN. Another issue is that they may not allow tunneling unless on a different contract.
What may be best for you is to ask the provider to use a specific APN for machine to machine, as those often allow intermobile traffic, are transparent and are likely to allow fixed addresses.