Kim's full delegation has not yet been confirmed, but other prominent North Korean officials seen in photos included foreign minister Ri Yong Ho and Kim Chang Son - the man who has been in Singapore in recent weeks negotiating logistical details for the summit.
The State Department is declining to release any additional information about the calls.
President Trump (3rd R) shakes hands with North Korean leader Kim Jong Un (3rd L) as they sit down with their respective delegations for the U.S.
Gorka agreed with Brian Kilmeade on "Fox & Friends" that the nuclear weapons agreement should be submitted as a verifiable treaty. There was no proof, though, that this suspension were permanent rather than a simple freezing of activity while Kim negotiated with other countries like South Korea and the U.S.
Amid the promises of de-nuclearization, security, peace on the Korean peninsula, and returning the remains of USA soldiers from the Korean War, there was no mention anywhere of human rights. The president's comments and face-to-face meeting with Kim have sparked criticism that he could legitimize or embolden North Korea's regime.
Trump Is Finally Meeting with Kim Jong-un
The diplomatic initiatives leading to the summit started in late April when Kim met South Korean President Moon Jae-in and the leaders of the rival states pledged to end hostility and establish peace on the Korean peninsula.
The summit, which was nearly scrapped by a mercurial Trump last month, comes after a flurry of diplomatic activities and barrage of invective and insults traded between the US President and an equally aggressive Kim.
But Trump told ABC News he believes that the trust is mutual.
At a solo press conference hours after the signing, Trump spelled out what kind of security guarantees he was talking about.
The carefully-choreographed signing went slightly off script when it appeared Kim's team did not want him to use the provided pen.
"While we should never refuse to speak with our adversaries, nether can we ignore the horrendous human rights abuses North Korea's leaders perpetrate against their own people. We're going to have a great discussion and will be tremendously successful".More news: How to watch Capitals Stanley Cup parade