Customer records are easily migrated by Vm2Mage from VirtueMart to Magento - including all their details (orders and addresses). However, there are a couple of things you need to know before starting off. This whitepaper deals with all customer-related topics with Vm2Mage.
The concept of an username is actually absent in Magento. Instead, a customer logs in using its email-address and a password. When migrating from VirtueMart to Magento this could mean that your customers need to deal with new login credentials. It's best to send out a mailing to your customer with a small procedure of how the login has changed.
Older versions of Joomla! store the passwords of customers as a MD5-checksum in the database. MD5 is used here as a simple encryption, but though it's quite popular, it's not extremely safe. Therefor newer Joomla! versions have introduced the concept of salted passwords, with which the regular MD5-checksum is accompanied by a little random string called the salt. The new salting mechanism used by Joomla! is incompatible with the similar salting mechanism of Magento. Plain MD5-checksums can directly be used with Magento.
New salted passwords from Joomla! can still be used within Magento by installing our free JoomlaPassword extension for Magento (available in the Vm2Mage download-section). While the Vm2Mage extension can be uninstalled after migration, this JoomlaPassword extension needs to be kept installed as long as your Magento users are using their old passwords.
Vm2Mage will migrate addresses as part of the customer migration. Addresses marked as billing addresses in VirtueMart will be migrated as billing addresses to Magento. The same applies to shipping addresses.
Migrating product reviews is part of the customer migration as well. Some information like rating is dropped, because the VirtueMart rating system is incompatible with the Magento equivalent. Because the Magento review-system requires a title and a nickname, a meaningless dash ("-") is used as title while the first name of the customer is picked as nickname.
Product reviews will be migrated again and again with each customer migration. If you migrate a customer twice, the customer record will be updated the second time, but the product reviews will be added twice.
If you have configured the Magento option Require Emails Confirmation to be Yes (under Customer Configuration > Create New Account Options), all new customer records will need to confirm their email before they are able to use their account. To skip this confirmation step for old Joomla! customers, make sure to migrate these customer records with the option set to No.
When you configure the Vm2Mage settings properly in Joomla!, you have made sure that the Store View is not empty. When it is empty, new customer records will be created within the Magento scope Admin. This still allows you to use those customers in the Magento frontend as long as the setting Share Customer Accounts under Customer Configuration > Account Sharing Options is set to Global. If you want this option to be set to Per Website, make sure to enter a valid Store View in Joomla! first.