I never have to put in anything, other than the amount to transfer and the payee (me). It could well be that when I first set it up a couple of years ago I had to have a number, but I don't recall that. I certainly don't have to do anything with BofA on these transfers, Transferwise debits the account and transfers the money.
I have Callcentric for my US phone. I used it while I was living there and I can take it wherever I go. It's $2.95 a month and if you don't want to mess around with an ATA to hook an actual telephone up to, you can get text messages by logging into the CC dashboard. CC can't do texts overseas yet (can't forward to a UK number) but you can send and receive texts "In the USA" by using the dashboard. It's pretty handy, as long as the internet is up! I have also used it to forward to my house phone here, and my daughter's cell when we are traveling. Again, they can't forward texts internationally, but the calls come through ok.