Found the solution.
On the Android simulator, the command Rho::RhoContact.find(:all) returns 'display_name', not 'first_name'.
Once I changed that command (person['display_name'] in my index.erb file, I could see the names of the contacts I had created.
At android you may use :select param with list of fields you need. In this case query may take longer time then with no params. In case no params only default fields are available for performance reason.