I have never seen this method of increasing the ringer volume in an AE 90. It must be extremely rare item! Too bad it is just a little sunburnt though.....Color code indicates it is a "Gardenia White" phone.
http://www.ebay.com/itm/261062862675
Terry
Hmm, looks about as neat as my home-made ringer box... :D
Now that you mention it, those holes don't look evenly spaced enough for it to be a factory job.
You only just noticed? :D
It is done well enough that with a quick glance it looks as though it could be a factory job. But afer studying it a bit more it becomes more obvious that it is a home brew job. Usually one starts to have trouble hearing the receiver rather than the bells on these phones!
Terry