using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var text = "Hey, whats up? You may call me at  if you wish. If, for some reason, that phone is bad for you - please try . And, of course,  is ok too.";

        var idx = new[] { 34, 108, 126};

        foreach(var segment in Split(text, idx))

        {

            Console.Write(segment);

            Console.Write("Открыть телефон");

        }

    }

    public static IEnumerable<string> Split(string text, int[] idx)

    {

        var startIdx = 0;

        Array.Sort(idx);

        for(var i = 0; i < idx.Length; i++)

        {

            var length = idx[i] - startIdx;

            yield return text.Substring(startIdx, length);

            startIdx = idx[i];

        }

    }

}