1.Ringtone

You can customize ringtone. And also you can add any songs coverted. Just export as iPhone format (AAC) from QuickTime, and change its extention to ".m4r". Then put it to the ringtone list in iTunes.

It' so easy, but sadly you can select ringtone only for phone ring and text message (SNS).

Customizing ringtone for other notice needs JailBreak.

2.Fetch (Push)

Push is setting for automatically transfering new data from servers like mobile me. If the server recieved new data, or data on the server is updated, it will be transfered to your iPhone.

Fetch is for apps which do not support Push. Automatically try to fetch new data from servers according to the schedule.

AIM seems to run as a background task updating its status, but you can not know its status without getting back to AIM.

AgileMessenger could be strong alternate of AIM. It shows the count of recieved messages on its icon polling the status. And it supports most of IM clients, WindowsMessnger, AIM, ICQ, YahooMessenger, and GoogleTalk. Installing AgileMessenger needs JailBreak though.

I am so much enchanted with JailBreak...