I spent yesterday morning in the garage doing a basic, but much needed workout. It was just a circuit of bodyweight and Kettlebell exercises after several rounds of jumping rope to warm up. Since I used my iPhone for music, the the Round Timer app took care of transitions. The app interrupts the music to announce round changes and then everything continues as normal.
I've been using the Round Timer app on my iPhone for about as long as I've had my Iphone. The company, Plain and Simple Software has made several improvements to the interface and stability of the app since its initial release. You can check out more details at the Apptism website
If you're someone that's training for rounds, doing circuit work, etc. this app is worth your 99 cents. With the level of customization you get, the app is competitive with the way more expensive round timer devices that can cost upwards of $10-100.
If your gym is like ours and uses an iPhone as part of its stereo, it may be worth working this into your system.
NOTE: I haven't tried getting it to work with Pandora's app, but it works fine with music played via iTunes.
That is all.
(have a good weekend)