I've seen this problem before. I don't text that much so I haven't had to deal with it. The problem occurs because of the long text messages. Standard text messages are limited to 160 characters. Some phones will allow sending a longer message and assumes the system will split the message into multiple 160-character limit messages and deliver each one separately. A glitch occurs when this process doesn't work and the message doesn't get split. Their system keeps trying to send the full message to you, which won't work since your phone can't handle it so it gets an error message and keeps trying. Eventually it will give up, but until then you cannot receive any new messages. Sometimes the new messages will get saved and delivered when the error clears, other times it just erases the message.

I don't know of a fix for this problem. Standard text messages were not meant for that so I wouldn't expect a fix from the carriers. You'll just have to live with it.