Well that may be, yet back in 2011 the application the company I worked for required sms verification (to prohibit multiple accounts) and the idea was to prefil

Well that may be, yet back in 2011 the application the company I worked for required sms verification (to prohibit multiple accounts) and the idea was to prefill the phone number reading that field. It totally didn't work and there were entries like '<unknown>' instead of null, etc. The application required Android 2.2 (iirc). The functionality was removed. Personally I have not seen an EU provider storing a real phone number there.