Is there any way to block objectionable ringback tones when calling US cellphones?

Do you mean the dial tone tunes that some providers let you get?

If so I always just complain to my friend, eventually enough of us were all giving him a hard time when he picked up that he just dropped the service LOL.

Nope!

In general ring tones are generated by the calling party's switching equipment. There is an exception to this that is exploited by ring-back tone provider equipment. The exception was originally provided to allow PBX equipment to provide busy/ringing/reorder signals.

I've looked at both AT&T (mobile and wireline) and Verizon (mobile only) ring-back tone products and both allow the subscriber to set specific ring tones for specific callers.

The person you are calling must be convinced to change their settings to accommodate your wishes.

I'm pretty obnoxious about my ring-back tones. My boss hears Janice Joplin belting out "Oh Lord won't you buy me a Mercedes Benz..." Special for him only.

Ever consider that your calling party might be messing with your head for grins?

Ever consider that ring-back tones are part of a person's fashion ensemble? Asking them to turn off ring tones might be like asking someone to wear different colored shoes.

I forgot - not everyone knows what a ring-back tone is.

When you call someone, the audible signal you hear when their phone is ringing is a ring-back tone.

When someone calls you, the audible signal you hear blaring from your telephone (mobile or wireline) is a ring tone.

Two of the carriers in Aus are now offering this as an option and I wish there was a way for me to stop it happening, but there just doesn't seem to be any way other than simply sending the person an SMS instead saying "Please call me".

This is all very discouraging; the person in question has truly bad taste in music.

Unless an opportunity to "reprogram" the offender's phone presents itself, I think that is what I'll have to do.