Hi Andriod,
To help you, we need more information.
1. Phone model (iPhone 3G/3G[S]/4/4S)
2. iOS version (I believe you already stated this as 5.1.1)
3. What you do to listen to the sermons and how site/phone behaves as a result (ie, I find the link in the speaker's section, click the 'Comments' link and finally click on the link to the sermon. The phone then shows the address from media.sermonindex…. I then get an error that says, "This format is not supported.")
If you've tried other methods, please tells us. They may reveal things not evident otherwise.
Have you tried using any other browsers, like Atomic, Mercury or Opera to play the sermons?
The Lord may also be telling you to be quiet before Him and know His voice because He wants you to rely on Him even more than you have up to this point.
A personal testimony, a few months ago I was lead to reformat my computer and get rid of the extra stuff, inlcuding sermons from the basic install. It was a clean machine as it were. I did make a back up of the previous contents onto an external drive. I have been blessed to have an iPhone and iPad which especially for the last few months have been my primary computing platforms. In the meantime though, I was lead to purchase a flashdrives to back up just the sermons, no applications, documents or even photos from over the years. Just the sermons. A few weeks ago while visiting a friend, I was carrying my laptop and basically all my computing tech in my backpack. He took me around to a few places on his scooter that evening, however, right at the end, when he was parking on an uphill slope, I jumped off like normal but lost my balance falling directly backwards landing on my external hard drive, laptop, iPad and so forth. At the time I thought to myself that it probably damaged my hard drive but the laptop should be fine. When I got around to examining the laptop and hard drive, I found that the screen on the laptop was cracked and only about 60% displayed an image but the screen itself was dimming quickly. When I tried to connect the hard drive, it didn't work at all. My iPad survived well and I was lead to put the flash drives in my front pocket so they survived too but the laptop and hard drive are done. In the past year, the Lord removed other things from my life that were good but from something I was finished with. I had asked Him about my laptop which was also from this period but He didn't tell me to get rid of it. In His time, He got rid of it. Although it is useful there was no pain in it. God is the source of life, my life, not sermons, not iPhones, laptops or any other thing. If I walk according to the Spirit, I will know Life and be free and full of joy therein.
EDIT: Testimony added