Virgin Mobile phone sends same text message over and over again

Okay, so my friend has a prepaid cellphone from Virgin Mobile.

Sometimes we'll be having a conversation, and then something happens with the phone service or whatever, and I get the same text message maybe 20 times over the course of 5 hours or so, and during that time she can't receive any texts from me.

Then after a while, it goes back to normal, and her phone gets a flood of texts that I sent over the past few hours.
What the heck is going on?
Why does this happen?
Can we do anything to fix it?

I'm not so sure how cellphone SMS messages work exactly, so I would love some more information.
Is anyone else having this problem or had this problem in the past?

Did you check with Virgin Mobile?

http://www.virginmobileusa.com/help-support

I did look there.
I didn't find anything... so unless I missed something outright... I don't foresee their site being all that useful.

How to contact Virgin Mobile.

http://www1.virginmobileusa.com/about/prepareEmailUs.do