Don't tip your hand
Check the whois for the .com domain to see when it was registered and will expire. If it was regged within the last one or two years and is not being used now, then they might not renew it. Also, your calling them might add value to the domain in their minds and cause them to renew it or sell it to you at a value-added price.
I'd say go ahead and reg both the .net and .us and use whois privacy until you resolve their renewal possibility or the issue of their selling their domain to you after they renew it. If you can, also hold off on putting up a website with your .net/,us domain.
There's always light at the end of the tunnel. Sometimes, despite lengthy registration periods, the registrant fails to renew it. Don't tip your hand just yet.
(RobertName).com was regged for two years. I wanted it badly and the other TLD's were available, as well as (BobName).com. I didn't contact them and just waited it out. I ended up getting (RobertName).com for reg fee.