Wetblanket, my perception of one of the other threads was that you had a problem, and some of the other posters felt the majority of your frustration was because you didn't like your co-workers and therefore "everything they do is wrong" from your standpoint. It wasn't something you said directly, just something other posters interpreted.
MadMadge, I think this is a very touchy subject, and I wouldn't approach it unless I had a) proof that this is the reason people are hanging up on him (recorded calls of accusations "You're in India" or something), and b) discussed this with the HR director, company attorney, or someone else responsible for the company's legal well-being. Don't name names, just explain the problem in a general way - one employee's accent is leading customers to believe he isn't American and therefore they don't want to do business with him, and you're just making sure it's okay to ask him to identify your city if he feels it would help.
If you can do both of those, then talk to PC in private and make it *entirely optional* that he does this. Let him use his judgement whether revealing this information would help or not for each call - and then you can rate his sales like you do for everyone else. If he gets mad that you're "racist" and refuses to say it, and his sales suffer, then you are justified in letting him go for his low sales numbers.
HR may have another suggestion, depending on your company size and makeup. Ultimately, you will have passed the buck to someone who will be accountable if he accuses racism, and you will have done your best to raise PC's sales so he's benefiting the company the same amount the other employees are.