Thanks everyone. I'm reluctant to use the "I must get off the phone because of cooker/kids" type of tips, because she would twig and anyway she rings me back an hour or so later with "Are you free now?" so it's much better to be honest.
The thing is, I really have been honest, and although it is a good solid friendship I'm beginning to think that she measures its value by how long I spend on the phone with her, even though she knows about my phone phobia. That judgement upsets me. I know she hates email and facebook but I don't judge her for very rarely (twice a year?) emailing me or getting in touch via facebook.
It feels a bit like she rings me when she's bored in the hopes that I'll entertain her (i know lots of people do this, even I do this with friends sometimes, but 90 minutes? It's like saying "Please stop everything and entertain me for the length of your average feature film.". While she's on the phone she'll say "Hang on, I'm just going to make a drink," or "Bear with me a minute while I put the washing machine on," and I just think - hang on - you've phoned me and stopped my evening. I am sitting here and my evening can't continue until you stop talking. Am I really expected to sit here and be background music for you while you do other things?
Also, I will sometimes say after about 25 minutes, "Okay, I'm reaching my phone limit now, ha ha you know what I'm like, I'm going to have to go in a minute," and she'll say "Okay then, I'm pleased you had a good week, it sounds much better than mine, oh did I tell you about the palaver with the gas man on Tuesday..."
Ten minutes later I say "Well, anyway, I've got lots to get on with this evening and I'm almost talked out so must go," and she'll say "No worries mate. I'm glad you've had a good couple of days, anyway. Let me have the details of that wildlife you went to, it sounds much better than our local one. You know last time we went there was this monkey...."
Ten minutes later I say, "Right, third time now mate, I really have got to go, we've been on the phone nearly an hour and I still ahve loads of housework to do, so it's bye from me!" and she'll say "Okay then, been nice chatting to you anyway. I wish we could just get together and chat any time, it would be so much nicer. I mean when I first moved here - have I ever told you this? - I was so worried that..."
Ten minutes later..!
She just DOES NOT want to have a call ended. Even after ages I get the sad little "Ah well I suppose it has been nearly 2 hours. I suppose we should go, I know you don't like the phone, but this has been ace, hasn't it, a lovely long chat like this?" and so even after spending hours talking I'm always left feeling inadequate.
She really does have a rhino skin on this. I think she thinks that one day I will see the light and start wanting hours on the phone and is just holding out for that day. Perhaps I should let her see this thread, she's enough of a mate to take it well I think!