1. After the firmware update 4, you do not need to convert your N73 to the Music Edition. There is no difference between the two. Just make sure you are running v4. On the standby screen, press *#0000# . If it says v4, then be assured. You have all the features of Music Edition.
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Nokia N73 SMS Accelerator. But what your problem concerns not hanging but a lot of time taken. When you change the phone memory, wait for 5 10 minutes before checking if the phone is working all right. If you already have a lot of mails in the memory card, it shall take even more time.