Hi, Simon
Answers to your questions:-
1) I thinks this is a common advice from cellular salesmen to ask their customers to charge their new phones for 10 hrs before use. Based on my understanding, Lithium battery is not required to charge that long in order to 'activate' it.
2) Serene mobile support GSM 1900. It will works in US as long as the mobile carrier use GSM1900.
3) I have both Mac OS and Vista in my iMac. However, I can't tell because I always have problems to transfer music with iTunes (Mac version). Example, songs are transferred but did not show up in the Music Library. In my opinion, this is easier to transfer music with Beoplayer in Windows system, if available to you. In addition, I do prefer Lossless files. Serenata did not support Apple Lossless. This is another reason why I use Beoplayer to transfer musics under Windows system.