WTA is not supported in current Nokia WAP enabled terminals as they are WAP 1.1 compliant, and the WTA features are coming with WAP 1.2 specification.
In year 2001 there will be two phones supporting WAP 1.2.1 and WTAI public library. Nokia 8310 is in the market Q3/01 and Nokia 6310 is in the market Q4/01.
However, Nokia 71xx and 62xx phones have a specific "Use Number" feature (behind the Option button), which you can use to "pick" a phone number on a WML deck, and setup a call to it. However, this is not anyhow related to WAP.