You can normally use the local SIM to call the US. Rates will vary and you should be able to research in advance. I've been able to call the US for as low as $0.02 per minute with a local SIM in certain Asian countries.

Prices, vary, however so it pays to check first and ask specific questions
on pricing.

Unlocking the phone on arrival may prove inconvenient. It's best to have it
done in advance.

An even cheaper option is to use Skype. Given the time difference between Dubai and the US you can arrange to be in your hotel room at most times when you will want to call the US. To call another Skype user the service is free. To call a US landline it's about $0.02 per minute.