From Forum Nokia Wiki

ID	KIJ000422	Creation date	October 5, 2006 Updated December 29, 2006
Platform	S60 3rd Edition Series 80 2nd Edition	Devices	All devices with firmware version earlier than X.0612.XX.XX Nokia 9300i, corrected in Nokia 9300i 6.27 build
Category		Subcategory

Keywords (APIs, classes, methods, functions):

Overview

When using the FileConnection API to write data to a file on a memory card on early S60 3rd Edition devices, writing is many times slower than writing to the internal phone memory.

Solution

This issue has been corrected in all devices with firmware builds which have version number X.0612.XX.XX (week 12, 2006) or later (check the 4 digits after the first point).