I have a similar problem with my BlackBerry Curve 9360 OS7 phone using PAYG.
I texted 789030 for a £2 weekly pass but by the next day I was still unable to set up email. (As Luke says, the Host Routing Table is blank.)
I did phone 789 but the lady there was unable even to see my text to 789030 or the text reply from Virgin saying that my Blackberry services were being set up.
She also said that nothing else needed to be done apart from texting 789030. She said there was nothing else that they needed to do at their end, which contradicts what Stephen_B said.
In the end, she credited my account for the £2 that had been debited & told me to try again. I re-texted but still no success. ( After re-texting, £2 was again deducted - but oddly a few minutes later my balance then went UP by £1 shortly after.)
The email account management screen on my phone still says "Unable to open email set-up application. Contact your wireless service provider."
I've been without blackberry services for over 2 weeks now and after two separate 90 minute sessions with customer services/technical I'm still without them. At the end of the second session I was told that the issue was to do with server maintenance involving 'blueyonder' and 'ntl' email addresses. I was told that once this maintenance was complete (they couldn't tell me when), the services would return. Quite frankly though after a combined 3 hours on the phone, they could've told me anything.
Thankfully I'm now in a position to take my business elsewhere because the sheer dread of another phone call to sort this out is about as appealing as root canal treatment.