Signal is open source (and non profit) and everyone can check what it is doing under the hood. Currently the number is used for sending the verification code.
I know I posted that myself except for the open source code which you can look at yes. You still have to use a mobile phone number which goes against anything they want to do in my opinion.
I am just saying that nothing is for free and someday Signal will fuck up too. If people really change to Signal (Millions) they will have to pay a ton of more money. Servers are not for free and if people don't donate they will get into trouble someday.
Sorry I know the Signal developer has a great mind and is all for privacy seeing the Facebook debacle back then when they bought WhatsApp, but expectations should still be low for the future. It's also always funny when something like this comes out and people still use their Android phones with shit apps or Google Mail and all and think they still have privacy. Not to mention surfing here, on Twitter, Reddit or any other site with Share Widgets on the bottom.