This is a good question at the moment, with both CRM and AX been growing products and AX 2009 providing an enhanced CRM module - the main reasons to use CRM rather than AX CRM seem to be the following:
- 100% Web-based whereabouts AX is a mixture
- Mobility is stronger in CRM with the ability to take your data offline via Outlook
- Marketing functionality
You may find the following quotations useful in deciding between the two products:
"AX CRM has been enhanced a lot," said Dane Koepke, head of business development at Green Beacon Solutions, a Microsoft partner, at a presentation last week to users at a Dynamic Communities AX Users Group session. It can assign sales territories, integrate with contacts in Outlook, and helps monitor the sales process.
For users who are uncertain what to do, it makes sense to try the CRM function in AX 2009, he said. "If it doesn't work out, you can go to CRM 4.0 and integrate" AX 2009 and CRM 4.0, Koepke said.
He predicted, though, that most businesses will find the CRM function in AX unsatisfactory. For his own marketing needs, he said, "I could not live in it. It's too broad."
Koepke's colleague, Richard Smith, an expert in Dynamics CRM, echoed that assessment. The AX CRM product "is a different product" from Dynamics CRM. It is designed for companies with a small sales team--for example, manufacturers in which the sales people are focused on meshing purchase orders with production capacity.
Kees Hertogh, Microsoft's director of Dynamics AX Product Management, seconds that view. The AX version of CRM is best for companies in which sales, promotion, and production "have a tighter connection into other processes, like quoting and maintenance." But "companies with large mobile sales forces" are likely best off with CRM 4.0, he added.
(Taken from http://msdynamicsworld.com/story/customer-relationship-mgmt/how-much-reliance-should-microsoft-dynamics-ax-2009-users-expect-pl)
The best advice however, would be to work with a partner that has strong AX and CRM experience who will be able to architect your solution based on your requirements and their experience using both products. Hope that helps.
Given that this will be a question for many people working with AX in the future, if you find any other resources that provide comparative information between the two products, it would be worth posting here.
Kind Regards, Paul.
CRM Consultant.