Já tentou?
If txtQuemChamou.Caption <> "" Then
Dim Formulario As Form
Set Formulario = Forms.Name(txtQuemChamou.Caption)
Formulario.Visible = True
End If
ou
If txtQuemChamou.Caption <> "" Then
Dim Formulario As Form
Formulario.Name = txtQuemChamou.Caption
Set Formulario = Forms
Formulario.Visible = True
End If
vlu//
ou