It's not just if the item is out of stock that you are liable to get ignored, but also often if it is in stock but just not available in the studio on that particular day. Sometimes you do get answered on air; but unless the answer comes very quickly you can miss it. It is absolutely maddening.
I always e-mail rather than texting - I don't "do" texts - and occasionally I get a really helpful reply back; it seems to depend on who's producing. I wish they would adopt a policy of always replying to e-mails if an item isn't available, so you're not left hanging on waiting, wondering what is happening.