[header] How to find the number of a blocked call [title] Get an private branch exchange (pbx) account. [step] One option is asterisk, a free, open source software. Another is switchvox. 
A pbx converts your computer into a telecommunications device and will allow you to manipulate incoming call data to identify blocked callers. [substeps] Before embarking on this method ensure that you thoroughly understand the technical challenge it presents and the potential financial burden it incurs.