SOLVED. Children's Book Set in Early 1900's [s]

[Jenny]

I read this book when I was 9 or 10, in the mid-1990s. It is about 3 girlfriends, I believe in the mid-west and maybe two are cousins (I think), set in the early 1900's. I remember something about a hill overlooking the town or one of the friend's two story house; also, a tree house and new invention of the telephone were mentioned. This is all I got; I am sorry but I need to know because it is driving me mad.
Thank you to everyone who tries to figure this one out.

[Mindy]

I guess Betsy-Tacy is too obvious but I'll say it anyway.

[Jenny]

Betsy-Tacy and Tib!!!! Yes thank you so much.

[Kris]

Betsy-Tacy for the link.

[Mindy]

Oh my goodness, hooray!