Recommendations for a datasync scenario ?

Hello good folks,

Our php application uses browser clients and magnetic card readers to collect
workmen's working times from a number of physical construction or project
sites to the main database at the head office, which is online with a private
ip-address.

Now we have a situation where not all construction sites' offices are online
or have so poor / instable connections that we can't rely on them. So we need
to install a local server to collect the data.

What would be a proper way to load the work time data up to the main database
when a local server is online again ?

Also, all the workers and sites are created and maintained at the head office
so we need to get this data down. There may / will be corrections to the
uploaded work time data as well.

I imagine all this could be done with unique row identifiers, temp tables and
shell- / sql-scripts, but why re-invent the wheel ...

All servers are linux + Pg8.2.

I followed the recent thread about 'replication in Postgres' but still any
info on experience of similar circumstances and pointers / comments /
recommendations are more than welcome.

BR,
--
Aarni Ruuhimäki