On every mobile back there is a rubber circular part with a pinhole at its center wat is that thing ?

Question

To mobile experts

Answer 1

It's for an optional antenna. The rubber plug can be taken out and a larger antenna plugged in.

Seems to be seldom used however.

Answer 2

"More Slack" is correct. It is a used to bypass the internal antenna to connect to an external antenna.  For some phones there are car mounting kits that makes use of this and connects to an external car antenna.  Almost nobody uses this these days as cellular coverage has gotten to be very good in most densely populated areas.  This is thru the installation of more cell-sites in the network.

So why keep the funny rubber plug and connector as it adds cost to the product?  It depends on the phone manufacturer, Nokia phones does not seem to have this.  Main reason is for final manufacture testing.  When thousands of phones are made in a factory and tested at the same time, it is hard to determine that a phone can transmit correctly over the air.  So test equipment connects to the antenna port, bypassing the internal antenna for the test.

Answer 3

OK, just what is a Mobile?...  A mobile phone, a decorative mobile that hangs  from a ceiling??..What are you talking about???

Answer 4

re set button.