Romans 10:9-13 (ESV)
9 because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.
10 For with the heart one believes and is justified, and with the mouth one confesses and is saved.
11 For the Scripture says, "Everyone who believes in him will not be put to shame."
12 For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him.
13 For "everyone who calls on the name of the Lord will be saved."
The Apostle Paul applies Joel 2:32, originally about Yahweh, to Jesus in verse 13. This identifies Jesus as Yahweh.
In this passage, the Apostle Paul teaches that Joel 2:32 has an additional application to Jesus, as He has been exalted by the Father to Lordship (Acts 2:36, 5:31, Ephesians 1:20-22, Philippians 2:9-11, etc.). The passage itself, however, clearly distinguishes between God and Jesus (Romans 10:9).
As is the case with each Old Testament passage which originally referred to Yahweh, and is applied in some way to Jesus by the New Testament authors, this passage never actually says that Jesus is Yahweh. Instead, passages about Yahweh can be said to be fulfilled in Jesus, because it is the consistent teaching of the New Testament that God was in Christ to a degree that is unparalleled. To this end, Scripture says that Jesus is the "image of God" (2 Corinthians 4:4, Colossians 1:13-15), the "express image of his person" (Hebrews 1:3), that "God was in Christ, reconciling the world unto himself" (2 Corinthians 5:19), and that "in him dwells all the fullness of deity bodily" (Colossians 2:9). This closeness is to the extent that Jesus can say, "He who has seen me has seen the Father" (John 14:9), and "He who sees me sees him who sent me" (John 12:45).
Therefore, texts which spoke of Yahweh doing something can be fulfilled in Jesus, because Jesus is God's agent and representative, through whom He works (John 5:19-20, 10:32, 10:37-38, 14:10-11). God can ordain an agent, and delegate whichever prerogatives or privileges which He sees fit to bestow upon Him. This does not take anything away from God, because His agent was established entirely by Him, and all honor given to the agent is ultimately to the glory of God (Philippians 2:11).