I recently switched back to the stock voicemail app that comes with the HTC EVO 4G, and it didn't take long for me to be bothered by the Voicemail-to-Text trial button that is always there. It doesn't really get in the way of doing anything and maybe it doesn't bug you, but I personally think it's a little annoying to see it all the time.
Thanks to my cheek, however, I found out that you can easily remove this button and make your voicemail screen look a little less cluttered.
All you have to do is long press right below the "Try Voicemail-to-Text FREE" trial button on the voicemail screen. A pop-up will appear that will let you select "Hide Free trial button." Tap it, and it's gone!