Current mobile devices such as mobile phones and PDAs are able to run applications that can demand a considerable storage space. When these devices run out of local memory, they require backing up their files in an external storage device, which could restrict the user mobility. This paper presents an Adaptive File Transfer Middleware (AFTM) for mobile applications. This middleware eases the transfer of files between a mobile device and an external storage server by accessing the best wireless connection (WiFi, GPRS/UMTS) available, considering quality and cost of the service. AFTM is also able to use the Multimedia Messaging Service (MMS) as another option for transferring files. A File Backup Service (FBS) was built on top of the AFTM. The FBS will detect when the device ran out of local memory and will automatically send selected files from the mobile device to an external storage server, freeing the mobile storage memory. To decide which files should be backed up, FBS implements several file replacement policies. Results showed that the selection of one replacement policy will be a trade-off between the efficiency of the algorithm and the cost of the wireless service available when a file needs to be backed up.
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