try this
Sub Main()
Using myreader As StreamReader = New StreamReader("
C:\Users\Jamiebones\Desktop\learning_application\learning_application\Phone Number.txt")
While Not (myreader.EndOfStream)
Dim line As String = myreader.ReadLine.Trim
Dim strBuilder As New Text.StringBuilder
If String.IsNullOrEmpty(line) = False AndAlso line.Length > 1 Then
strBuilder.Append("234")
strBuilder.Append(line.Remove(0, 1))
End If
Console.WriteLine(strBuilder.ToString)
End While
Console.ReadLine()
End Using
End Sub