HeatherS,
For a small amount like $600, I would bring the whole thing in cash with an ATM card for a backup. I would not waste my time getting traveller's checks, finding a place to cash them, etc. for that amount.
It should consist of 5 $100 bills and small stuff. That will make it easy to carry/conceal. KEEP NO MORE THAN $200 in your purse/wallet - the rest in an inner pocket.
Be sure that you can make $10 in change to buy the tourist card. Also, be able to pay airport tips with an assortment of $1 bills, and be able to come up with $18-20 to pay the cabbie in Santo Domingo or Puerto Plata (much less in Santiago).
Of course you will change $200 to pesos the first time you visit an exchange house. Don't change it all at 1 time of course because with the peso being even weaker than the dollar, you might get a better rate tomorrow. Also, you don't want to wind up with way too many pesos.
The best way to telephone home is from a call center. They are everywhere in the towns, although maybe not in the all-inclusives. The cheapest is Turitel. Unfortunately, although their signs still stand, most of their locations are no longer active. Tricom is 2nd best and very numerous. Its rate to the US is in the range of about 6 pesos per minute. BTW, if you need to call an 800 number, you can do so by dialing 880 instead. You cannot call an 800 number at all from Turitel (nor even a Dominican one, I think - international only).
Have fun.