Rav Yitzchak Zilbershtein, rav of Ramat Elchnonon neighborhood of Bnei Braq, was asked about the laws of yichud -of a man and unrelated woman being in private together. While we have an allowance in a situation in which the woman's husband is in town, because he might come home at any time so that fear of him walking in the door would prevent her from doing anything improper with the strange unrelated male, perhaps today that no longer applies. Why would it not apply? If the husband has a cellphone, a smartphone more specifically, the wife can usually track the husband and know where he is. If she knows where he is at all times, or can know, perhaps she has no fear of him walking through the door, as she can check at any time if he is on his way home and how far away he is and how much time he has. If she does not have that fear because she knows, she is not prevented from anything improper with a male guest, so maybe that hetter no longer applies?

Rav Zilbershtein responded that regarding the allowance of the husband being int own there is a machloket, if she knows he wont be home any time soon. Rav Zilbershtein said the Chazon Ish said the hetter still applies because she has a natural innate fear of himwalking in and Rav Elyashiv said it does not apply in these situations. Rav Zilbershtein said one should be machmir in such a situation, especially as not everyone agrees to the allowance in the first place.

source: Hamechadesh

I would note that he does not say that having these smartphones is assur, just deals with the specific question. 

This question would not apply to kosher phones, as they cannot really be tracked so she would never know if he is on his way home or not by location tracking.

This might be a good example of the evolution of halacha, how a new reality affects the accepted halacha on a matter.