You can use Exchange 2010 server with different URLs for internal and external access – but this configuration can get in conflict with your SSL certificate. Internal host names are mostly not allowed in public SSL certs, and Exchange allows only 1 certificate to be active for one service. Note that the SSL certificate policies get even more restrictive in the next few years.
You can get a certificate which allows internal domain names, but I would not recommend this way.
Better forget the internal URLs and use the external URLs also for internal access.
DigiCert offers a free useful tool for the modification (even if your certificate is not from DigiCert). It also creates a rollback script.
You can also optimize your internal Windows DNS server to recognize your external domains to be internal (otherwise your internet router would have to do this job).