Updating Hosted database from remote database

We have a database hosted with Filemaker server 9 advanced, we have a volume license for Filemaker 9 for the laptops in the field. We wanted to have everyone just work remotely using their aircards. The problem is their field work is done from hospitals, there is usually no signal. So plan b is that each user will have a copy of the database on their laptop and when they get home at night they can remote into to the remote database and run a script to update the records that have changed. I need to write a script to do this but I was wondering if there is some trick to synching.... is there a plugin or something to make this process simpler? I'm worried about data integerity.

Any help would be greatly appreciated.