Let's just imagine that you've a website. And your website is fancy enough to integrate with another system - say your shiny new CRM system or ecommerce store. Let's say you've organised hosting for your website. All is well, everything works.
Well, works for a while ... but then, disaster strikes! You notice that your ecommerce transactions are not making it into your CRM. Who do you call? Is it the web developers? The CRM vendors? The hosting provider? Your telecoms provider?