Concatenate strings with vb6

I am trying to concatenate in vb6. The operator += is not supported, and I want to do something like the code below. I want to add more strings to a textbox as the program works down this code. Can anyone advise what to change += to? I know & can be used when adding one string to another, but it the example I am working on here, that doesn't seem suitable.

Thanks.

    If (strHomeNo <> "") Then
        txtPhoneNums = "Home: " + strHomeNo
    End If
    If (strMobileNo <> "") Then
        txtPhoneNums += "Mobile: " + strMobileNo
    End If
    If (strWorkNo <> "") Then
        txtPhoneNums += "Work: " + strWorkNo
    End If
    If (txtPhoneNums <> "") Then
        txtPhoneNums.ForeColor = vbBlack
        txtPhoneNums.FontBold = False
    End If
Else
     txtPhoneNums.Text = "NO CONTACT DETAILS"
     txtPhoneNums.ForeColor = vbRed
     txtPhoneNums.FontBold = True

would :

txtPhoneNums = txtPhoneNums & "Work: " & strWorkNo

not work?