Automatically add country code to phone numbers in vCalendar File wherever that is absent (I wrote it after moving to USA from India). Minor changes may be needed for different cases/countries/versions of VCF. As I only found paid apps for this, I wrote this one after analysing patterns for about 2 hours.

phoneCountryCode.py

import re

with open('PIM00004.vcf', 'r') as f:
    vcfText = f.read()

regex = re.compile(r'[0-9-]+')

regexPhoneNumbers = regex.findall(vcfText)

for eachRegexPhoneNumber in regexPhoneNumbers:
	tenDigitPhoneNumber = eachRegexPhoneNumber.replace("-", "").replace(" ", "").replace("(", "").replace(")", "")
	if len(tenDigitPhoneNumber) == 10:
		phoneNumber = "+91" + tenDigitPhoneNumber
		vcfText = vcfText.replace(eachRegexPhoneNumber, phoneNumber)

with open('contacts.vcf', 'w') as f:
    f.write(vcfText)

Also, I allow this particular Github Gist code to be used in any proprietary/free/open-source/closed-source/military applications. However, I am not liable for any of the negative consequences of the usage of the aforementioned code.

Also, the code is nice and short because, I have used the property of unique phone numbers. However, if that changes (multiple people owning same phone number with different formats including hyphens and spaces) in the future versions of VCF file (which I strongly believe won't happen), then, in that rare case, the aforementioned code might not work.