I to wondered this an have a solution that worked for me with Android notifications but I don't know about blackberry
First what I did was search and found a converter called iringer. It can convert files that you have into ringtones. (I have a ringtone app maker on my iPhone by found that I I want to make a short SMS tone it won let me so iringer will let you make a notification.
Now when I had Android I use to use zedge for all my notification tones and I would directly install them onto my iPhone. But since the iPhone doesn't have the app or won't allow you to directly install into the phone I went to the desktop version of zedge on my pc.
There I searched for the tone I wanted. When you find the tone you want you download with the option to download directly to pc. Once you do that you open up iringer and there is only three options, import,play and export.
First you import the song which lets you locate the zedge song you downloaded then you play it and see if you like it. Next you import it. It gives you three options and click on the one where it says to send to iTunes. It should concert quickly and give you a message telling you it's imported. Next ou heck under our tones in iTunes and it shoul be there. Hook up your iPhone and go under ringtones and sync it and bam when you go under sounds and it should be there.
Hopefully I wasn't to confusing if I was feel free to ask me any questions and I'll try to explain more In depth as I was getting ready to go to work and thought I answer before I left. Hopefully it helps.