In fact, what you want to achieve is made in the program flow.
If you separate the subs correctly you can check if the SmsDelivered event (PhoneEvents) has fired and if it was the last message to send. Then in the same event when the condition was met, call another sub and so on.
Sub Process_Globals
Dim Psms As PhoneSms
Dim PE As PhoneEvents
end sub
sub XXX_click
PE.Initialize("PE")
Psms.Send2("121344564","message",true,true)
end sub
Sub PE_SmsDelivered (PhoneNumber As String, Intent As Intent)
' this is deliveri status check
end sub
Sub PE_SmsSentStatus (Success As Boolean, ErrorMessage As String, PhoneNumber As String, Intent As Intent)
' this sendi,n complate status
end sub
'ENVIAR SMS VIA INTENT
Sub Enviar_SMS(numero As String,texto As String)
Try
Dim In As Intent
In.Initialize(In.ACTION_VIEW, "sms:" & numero)
In.PutExtra("sms_body", texto)
StartActivity(In)
Catch
Log(LastException)
End Try
End Sub