It can get "fun" sometimes at stadiums, etc. with ISDN lines or even POTS. Since sports is long-form, when crap doesn't work it becomes a pretty big firedrill to "fix" the problem quickly. Many networks use ISDN and primary and POTS codecs as the backup. In some places the ISDN lines won't work for one reason or another and the POTS lines won't work right, many times due to the univeristy running them through their phone system which is actualy VOIP. Hopefully some of the networks are exploring 3G as a third option, but I bet plenty of them still don't have an option #3 even. Many of them only have option #1.
I haven't used phone lines (POTS or ISDN) on remotes for at least three years now. Cell phones are still crap, excessive compression and limited audio bandwidth. I understand KGAF in Gainesville has been using Skype for remotes (per Steve E.). Windows Media Encoder has been very effective and dependable. The station has the IP address, enters it in the WMPlayer 'Open URL' command and then pots it up on the air.
