Hmmm... "a strategy" or strategies... Don't meet up w/ them too often, plan a short visit when you do, end telephone conversations as quickly as possible, communicate (if you have to) mostly by text.
But this may be key...
"I'm the type of person who has never really "put my oar" in, so I tend to just make the usual noises and let them speak. Don't know why, it really annoyed me today, but I'd like a strategy!"
Perhaps, as others have suggested, these two other people feel they need to fill in the "space" you leave in the conversation. But maybe you suddenly felt "annoyed" b/c you're no longer content w/ this. So another strategy may be to put your oar in from now on after all. If it's hard to get a word in, well, I hate to say this, but, interrupt a few times, until they get the idea that Nantofran wants to contribute nowadays. It's rude, I know, but it may be worth showing them you're more assertive now/want to be an active part of the conversation.