Has anyone ever complained to Nextel about their sucky text messaging service and what did they do to fix it?

I have a Nextel phone (I 870), and when I send text messages to my friends, they get them right away, but those outside the Nextel service(i.e Verizon, Cingular) who send text messages to me, theirs can take up to several hours to reach my phone! I call Sprint/Nextel all the time and I keep getting the same runaround. They have told me to send voicemail messages "Urgent" to reset it, they have told me to turn the phone on and off, they told me it was my phone (and I was dumb enough to buy a new one), and I even had one tell me there is nothing they can do about it. I never had a problem until the last couple of months! Thanks!