It's pay as you go. Walk into the Claro office, and tell them you want a number with them. They'll give you a new sim card. The agent will also be able to scroll through the list of available numbers. If your's is free, you can have it. If not, you can choose any number you wish. I always had a problem remembering my number when I moved here, Claro allowed me to pick my number, and I made it a combination that I won't forget.
Step 1.- Your orange number must be a prepaid phone. If not tell orange you want to switch into prepaid service, because if is not prepaid will appears always that you owe money to Orange and will cancell the portability aplication.
Stop 2.- Go to claro customer service office and tell you want to port your orange number, they will ask you for your ID to make a copy and fill an aplication. You have to tell them if you wants a prepaid service with claro or postpaid. In case you want postpaid they will check if you have good credit record, after that will be wait 7 days, and your number will be in Claro, you will have to go back to pick up your new chip when your old chip go off.
I switched from VIVA to Claro, tired of waitting for 4G service almost 2 years ago, now finally VIVA is installing 3G and 4G, but Claro now has Roaming with the local minutes and data in 20 countries, so I stoped thinking to go back to VIVA.