Wirelessly posted (Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 8.12; MSIEMobile6.0) Sprint T7380)

theres been a handful of times that Ive tried to send a texst and it will say something about my phone needing to connect n Sim Card not ready. Has anyone gotten this error before? When that happens, the only way to send a text is to turn the phone off then back on. Any idedas on why it does that?