All of the above generally accept tapes only on the recommendation of their client advertising agency producers or casting directors. Sending unsolicited demos is not recommended. Ahh, grasshopper, that is the zen koan you must solve for yourself. All this talk about how very competitive this field can be is not meant to discourage you, but rather to inform you about the considerable challenges that face a newcomer. It is not impossible, however.
New voices break through every year.
I have had lots of help along the way, but my most valuable tools, perhaps even more than natural talent, have been persistence and consistent hard work. I did the work required to get myself prepared, then I simply refused to go away . Eventually, the industry gave up and let me come in to play, and for this, I am grateful. If you love this stuff, don't let anything stop you.