I did some testing with the new Google Chrome Click to Call Extension and noticed some flaws that are probably easy to fix. 1) Numbers with / in them (very common format in Germany) are not recognized. Example: 1234 / 56789 won't work. 2) There are several slightly different characters that can be used as a hyphen. However only one of them (Unicode: U+002D) will work for Click to Call. Of course there are also guidelines as to which character should be used in which situation. But most people who use a hyphen in their phone number either don't know or don't care and just randomly use one of them. So Click to Call should not care either and just accept all of them. Example that will work fine: 1234 - 56789 (Unicode: U+002D) Six very similar examples that won't be recognized as a phone number: 1234 ‐ 56789 (Unicode: U+2010) 1234 − 56789 (Unicode: U+2212) 1234 ‒ 56789 (Unicode: U+2012) 1234 – 56789 (Unicode: U+2013) 1234 — 56789 (Unicode: U+2014) 1234 ― 56789 (Unicode: U+2015) 3) Dates written in the format dd.mm.yyyy (most common format in Germany and probably also in other European countries) are recognized as phone numbers. Example: 15.08.2017 will be recognized as phone number. I never saw anyone use points in a phone number. So it's probably a good idea to ignore any number that has a point in it (just like it is now with slash or most kinds of hyphen where it should not be). 4) VAT Reg No and IBAN (eg. DE123456789) are recognized as phone number. Because these numbers generally tend to be listed in conjunction with phone numbers and other contact data at the same spot, it's probably a good idea to filter those out. I know that it is impossible to avoid false positive number recognition in some cases, but because of the very unique format of IBAN and VAT Reg No (all starting with two capital letters), a filter for this is probably quite easy to implement.