The best responce I have ever seen to a loud mouth phone user on the trains was this:
One young man on a train chatting really loudy, everyone in the carridge could hear him, not only that he was one of those people that repeated both sides of the conversation so we could basically could here the whole convo. So he was saying (one man remember) "hi darling how are you?, You're well!, Excellent good to hear, i am also fine. What are we having for dinner tonight?.... you want a takeaway! Oh lovely that sounds great, when do you want to go?, about 8 that sounds good to me....
You get the idea! Both side of the convo from a mouth of one man.
So these two women on the train, decided to go and sit either side of him..... ring one another, and have the same chat with each other. Again stating both sides of it! Once the man realised what was going on he went bright red and soon hung up.
The whole train was laughing and hopfully the man in question was never that annoying again.