Cannot call out after making a text

I am having a problem (well actually a friend is), with their 6680. When switched on, it can call out no problem. But, once a text is made, the phone will no longer call out (i.e. green, green has no effect). Can dial the number separately, but the stored outgoing phone numbers can no longer be accessed. Am I missing something here? Why should this stop working after a text message? I've tried a soft and a hard reset and the only thing I can think of is a firmware upgrade is needed?

Thanks in advance for any help!