well, u can also try enabling swap. it happens to me too sometimes, and enabling swap memory solves the issue. also, chk ur gprs provider's settings. as u mentioned this is more ofter the case with one particular provider, so the issue is with the gprs settings related to the service provider. hope, this solves the problem.
once upon a midnight dreary, while i pron surfed, weak and weary,
over many a strange and spurious site of 'hot xxx galore'.
While i clicked my fav'rite bookmark, suddenly there came a warning, and my heart was filled with mourning, mourning for my dear amour,
" 'Tis not possible!", i muttered, "give me back my free hardcore!"
quoth the server, 404.