The Amish community I know aren't super strict. They use gas farm equipment and are fine with solar batteries. They just don't want to be on the power grid.
The main cruxes tend to be: having a wired connection to "the grid"/outside world. Not being fully independent. Adopting worldly & not practical practices.
Cell phones are practical. I've seen a few Amish with basic cell phones at farmer shows.
yeah I remember awhile back. talking decade or so. that they were creeping in (cell phones) but there had not been an official ruling. Some had them but kept them outside of the house and such. I had actually saw one thing that said they would have like phonebooths at the intersection of several family farms and that was considered all right because they could share and would not be tempted to use it for poor reasons.