Why the GSM Shield is discontinued? What options are available? I need to build a device with a single button to make a call over a mobile network (GSM)

I wanted to buy an arduino one and an arduino gsm shield for this, but just noticed that the GSM Shield is retired - discontinued.

I checked all the arduino products but there is no options for integration with GSM.

What options do I've to build my products if the GSM Shields is discontinued?
A retired product is just a product that isn't supported anymore. It doesn't mean that this product is not usable anymore. Because the GSM shield is discontinued by Arduino.cc itself, you could buy Arduino.org (link to the GSM shield 2), or even an other model by Adafruit. Here is a link for many options of GSM shields on Adafruits' website.

A last option would be to buy it from a chinese seller on Amazon or Ebay. Though they are cheap, they are usualy very crappy and there are not many libraries for them.