Ask HN: When should we ask for credit card details?

Hey HN,

We (me and markbao) are Supportbreeze. We're working on our marketing pages now and we're not sure if it's better to ask for credit card details at signup or sometime after the trial expires. We know a lot of companies, like 37signals, ask at signup, but we don't have a free plan (for more on that, see here: http://news.ycombinator.com/item?id=1615416) and only offer the trial. So if we ask for credit card details, there is no way to trial our product without providing it. Will asking at signup deter people from trialing? Is it better to ask at signup or after trial expires?

Thanks.