I'd just like to give my experience, which varies to what you seem to be told as being the case on MN! I'm in London, but the overriding feeling I got was that whether you get given any free time or not varies from law firm to law firm, and to how busy the person you're speaking to happens to be at the time you call them.
I contacted overall probably about 6 different lawyers, from very high end ones (what was I thinking; starting price was £500ph - it was a very brief call) through to much cheaper provincial firms. The cheapest firm I contacted who mainly did legal aid work, charged me for a first appointment, about £200 for about 90 mins, although I did have a 20-30 min chat on the phone before making that face to face appt.
Nearly all lawyers I spoke to were very giving of their time on the phone, without being particularly prompted, giving me their 'at first glance' summary. The lawyer I chose in the end, a City firm, were the most impressive in terms of free time - he asked me to send through a summary of my situation by email so he could look at it in advance, and then we had a free initial appointment which was incredibly helpful.
Therefore I do think this idea of the free half hour is a bit odd. None of the lawyers I spoke to seemed to know about it as being a 'thing', and some of them were willing to see me for an appointment up front, some of them weren't. None of them wanted it to just be half an hour. And almost all of them were willing to talk on the phone before I even went in.
My advice would be to get recommendations if possible and then phone a few up and get a feel for them. Write down a summary of your situation in terms of finances etc and take that along with you. Good luck.