Yes, both are correct. You do have the ability to import contacts; you can export Google contacts to .csv, remove extraneous fields with Excel, and import them all into VoIP.ms' address book. Not sure whether Apple offers similar export functionality. If you use Android but don't sync with Google for some reason, there appear to be numerous apps for exporting contacts to various formats.

I should also note that the emailed text message includes a unique identifier in the subject that maps back to the source number from which the SMS was sent. That identifier appears to have a very long lifetime; I don't think they get recycled. It's technically possible to send a message to a contact that doesn't exist in your VoIP.ms address book by including that identifier (in the format "[#XXXXXXXXX]") in the subject and sending it to [email protected]. Of course you can also simply reply to a previous SMS sent from that individual to your VoIP.ms DID.

EDIT: There are both Android and Apple texting apps designed to use VoIP.ms' SMS API. They allow you to send texts to arbitrary numbers that are not stored in either your phone's contacts or the VoIP.ms address book. They're not replacements for your regular SMS app, though. The one I've tried is for Android: VoIP.ms SMS