It's simple to downgrade. However, I do have a workaround for the voicemail indicator, if you're interested...
YouMail - Cell Phone Voice Mail with Personalized Greetings and Online Retrieval
Works awesome! I get an email with a transcribed message of the voice message as well as a .wav attachment that I can listen to if I want to. I can also just call in and listen normally, too. I switched and I probably won't be switching back even after they fix the voicemail icon.