eisbaer I read your post with interest.
My Mum drives me crazy too. She's so self centred and self serving (she does have positive qualities too). But I am right with you on the irritation during phone calls, my Mum often eats while talking to me "It's OK MoonHare it's a one handed job" is what she says, she talks always for exactly an hour (because that's how long the call is free for) on times/dates that are most convenient for her, is frosty if for some reason I hadn't answered the phone when she had said she would be calling, she also talks for most of the hour about random people she is acquainted with who I have never met, there's always someone who has upset her in some way and she goes on about that. Often it's not even what she says but what she doesn't say or the way she says it, anyone once else listening would think it perfectly innocent and wonder why I was upset but she knows how to needle me in a passive aggressive way.
When she's in one of those moods (I can tell instantly by the way she says hello) then I find the way to make the calls work for me is to try to monopolise the conversation myself going on about my children/my friends or to ask lots of questions about the members of my family who live near her.
In spite of the above I am actually feeling much less irritated by her than I was approx. 18 months ago when I was also pregnant. I really do think being pregnant reduces your capacity for tolerance, plus there's something about being about to produce a child that makes you reflect on your own childhood and the sort of parenting you received. My Mum has her good points but overall she wasn't the best at parenting young children.
I think once your pregnancy hormones calm down you'll find it easier. The other thing for me was that (while I was pregnant) she and I had a huge row, started because I could not hold back and told her some home truths. She was being really mean about my long-suffering Dad and that's what made me snap. We didn't speak for 3 weeks, then she phoned me, she did not mention our row (nor has she ever since) and did not apologise but she has been much better and made more of an effort with my children since then. I now find I can take a deep breath and let most of it wash over me, because yes, I will miss her when she's gone.
Maybe you could take a deep breath and tell her how you feel (not 100% of how you feel but enough to get the point across) and then leave her to think it over for a while???
I have lurked on the 'stately homes thread' and the backgrounds of most posters on there do seem so much more extreme than mine I would feel like a fraud joining in.
eisbaer maybe we could start our own support thread - "My Mum drives me crazy by eating on the phone"!!??