The disclosure provides for a telecommunication method using a communication system, wherein the communication system comprises: a main database system; a local database system; a first network connection for exchanging data between the main database system and the local database system, wherein the main database system and the local database system are separated by a first firewall; a handheld telecommunications device with digital mobile telecommunication connection to the local database system. The method includes: receiving a document database by the main database system; receiving a set of permissions for the document database for a group of users; generating a local database instance on the local database system for an external user; copying user permissions from the main database system to the local database; copying a portion of the document database to the local database instance; sending a modification request from the handheld communication device to the local database system; and forwarding the modification request from the local database instance to the document database if the modification request is allowed by the user permissions; modifying the document database using the modification request from the local database system to the main database system if the modification request is allowed by the set of permissions; and synchronizing the portion of the document database with the modified document database through the first database tunnel.