Recently the use of cellphones and smartphones has met with a lot of criticism in some communities. I'd be interested to see if landline telephones encountered any similar opposition when they were first introduced. Can anyone point me to rabbinic responses to landlines?
To my knowledge there was no opposition to utilizing telephones when they were initially introduced, the difficulty is that this in itself does not mean that there was no opposition. Furthermore, if there was no opposition, it could be difficult to demonstrate this fact since it is unlikely anyone would write teshuvos on why they do not object to an item that no one considered objectionable. Nevertheless, it seems that most of the discussion about [land-line] telephones seem to focus on their status on Shabbos/Yom Tov or their the propriety of using them to fulfill halachic obligations regarding hearing or speaking, which may support the notion that their use wasn't considered problematic in itself. This is also further supported by the fact the functions preserved by the "Kosher" cell phones you mention are those of the land line.
In Israel you can own a kosher cell phone. This means that you have a constant monthly payment with a bank of minutes you can use to call other kosher phones and landline phones. Taking pictures, surfing, sending SMSs and so on are disabled on the phone. The calls to non-kosher cellphones are much more costly. Kosher cell phones are backed by Rabinical authorities.
(There are some more details about this (that could be found here); I'm just presenting the main idea.)
From the above I conclude that common practice in Israel is that any landline phone is equivalent to a kosher cellular phone. From this I cannot derive what happened when landlines were first introduced, but anyway I suppose they were not criticized.