In unity3D, Click = Touch?

Short answer: yes, touch may be handled with Input.GetMouseButtonDown().

• Input.GetMouseButtonDown(), Input.mousePosition, and associated functions work as tap on the touch screen (which is kind of odd, but welcome). If you don’t have a multi-touch game, this is a good way to keep the in-editor game functioning well while still keeping touch input for devices. ^{(source: Unity Community)}

• Mouse simulation with touches can be enabled/disabled with Input.simulateMouseWithTouches option. By default, this option is enabled.

• Though it is good for testing, I believe Input.GetTouch() should be used in production code (because it is able to handle simultaneous touches).

• Interesting approach is to add touch handling to OnMouseUp()/OnMouseDown() event:

    //  OnTouchDown.cs
    //  Allows "OnMouseDown()" events to work on the iPhone.
    //  Attach to the main camera.
  
    using UnityEngine;
    using System.Collections;
    using System.Collections.Generic;
  
    public class OnTouchDown : MonoBehaviour {
        void Update () {
            // Code for OnMouseDown in the iPhone. Unquote to test.
            RaycastHit hit = new RaycastHit();
            for (int i = 0; i < Input.touchCount; ++i)
                if (Input.GetTouch(i).phase.Equals(TouchPhase.Began)) {
                    // Construct a ray from the current touch coordinates
                    Ray ray = Camera.main.ScreenPointToRay(Input.GetTouch(i).position);
                    if (Physics.Raycast(ray, out hit))
                        hit.transform.gameObject.SendMessage("OnMouseDown");
                }
        }
    }
  

  ^{(source: Unity Answers)}

UPD.: There is Unity Remote mobile app for simulating touching in editor mode (works with Unity Editor 4 and Unity Editor 5).