So, today I did my first implementation of ActiveSync for an iPhone and I'm pleased to say it worked great when using a GoDaddy certificate.
For those of you that are not aware, GoDaddy sells 1-year domain validated certificates for about $30US while competitors often charge $150US or more. The only catch is that occasionally, some (typically older) applications or operating systems do not properly trust the GoDaddy certificates. However, I'm seeing this less and less. All of our recent (last year or two) Windows Mobile devices have been fine with GoDaddy certificates as well.