My SE Z600 have an old firmware because i buy it when it comes first. in my opinion the RF quality of SE Z600 is very bad! If i change the firmware with the latest firmware, it will rise the quality of RF? Please let me know...
I've heard that it can increase power to the antenna (at the expense of battery power). I've seen posts on AT&T forums about firmware updates to certain phones like the SE T616 that have proven to increase signal strength.