If both phones are active and the receiving phone is gsm then you have to call CS. Can't transfer to an active gsm online. You can transfer to an active cdma online or with CS.
If you want to transfer to an inactive phone you can do that online. Depends on what type of phones you are working with as to whether you have to transfer the number or not. Find all the info and tutorials on my links page HERE
Transferring from a newly activated phone is not recommended anymore, They have started turning off phones that receive transfers from phones that have never had any paid for minutes added to it.
There's no present. There's only the immediate future and the recent past. –George Carlin