@Danne: I think there's definitely a way for everyone to be happy here. The choice for wedding wear isn't tux or fancy gown anymore, there are plenty of formal-wear options these days. I think you should look for a formal trouser-suit, maybe in a gender-neutral (as society sees it) colour that makes it look "prettier" (women usually wear colours to a wedding) but isn't, like, frilly pink or something that's very girly to you. So maybe a nice understated blue trouser suit with a nice white shirt and no tie. If your mother still isn't happy, I say just go ahead and get in touch with the bride. Is your dislike of telephones greater than your dislike of wearing a dress/skirt for a whole day? If not, just go for it. Write down what you're going to say, and the number, on a sheet of paper. That way, you won't forget anything, especially if you have to leave a message. Tell the bride you don't like dresses, but you want to look nice for the wedding, and describe what trouser-based option you're thinking of wearing instead. Say you hope she doesn't mind you wearing that instead of a dress, and that you're looking forward to seeing her, or something else friendly.

It's not such a weird thing to dislike dresses these days. I have a cisfemale friend, who is straight, and pretty, wears her hair long, and just really doesn't like dresses. I've seen her in a dress once. It was for Hallowe'en, and she was wearing her jeans underneath it. She wears neat black trousers and nice shirts to formal occasions (there's another option for you!).