Since I am operating in a tourist area, where tourist from different european countries visit. So I added calling codes of almost all the countries in Settings > Customer APP > Default Country Code on Phone field:
If anyone interested you can copy from here.
+39, +49, +1, +7, +20, +27, +30, +31, +32, +33, +34, +36, , +40, +41, +43, +44, +45, +46, +47, +48, +51, +52, +53, +53, +54, +55, +56, +57, +58, +60, +61, +61, +62, +63, +64, +65, +66, +81, +82, +84, +86, +90, +91, +92, +93, +94, +95, +98, +212, +213, +216, +218, +220, +221, +222, +223, +224, +225, +226, +227, +229, +230, +231, +232, +233, +234, +235, +236, +237, +238, +239, +240, +241, +242, +243, +244, +245, +248, +249, +250, +251, +252, +253, +254, +255, +256, +257, +258, +260, +261, +262, +263, +264, +265, +266, +267, +268, +269, +269, +290, +291, +297, +298, +299, +350, +351, +352, +353, +354, +355, +356, +357, +358, +359, +370, +371, +372, +373, +374, +375, +376, +377, +378, +380, +385, +386, +387, +389, +418, +420, +421, +423, +500, +501, +502, +503, +504, +505, +506, +507, +508, +509, +590, +591, +592, +593, +594, +595, +596, +597, +598, +599, +670, +672, +672, +673, +674, +675, +676, +677, +678, +679, +680, +681, +682, +683, +685, +686, +687, +688, +689, +690, +691, +692, +850, +852, +853, +855, +856, +880, +886, +960, +961, +962, +963, +964, +965, +966, +967, +968, +970, +971, +972, +973, +974 , +975, +976, +977, +992, +993, +994, +995, +996, +998,
I have placed the Italy +39 in first place because I am operating in Italy
