The electricity is 110-120 VAC. It is advisable to bring a computer and buy other small appliances here. However, if you have a favorite small appliance and can fit it in your suitcase; you might want to bring it with you.
The cost of small appliances is slightly higher than in the US and there are some name brands. You might want to bring rechargeable batteries or smoke detectors. Lithium batteries are difficult to find.
Smartphones and regular cell phones can be used in Costa Rica. They have to be GSM compatible. If you aren't sure then check with your carrier to verify that your phone is a global phone. You will also need to have it unlocked by the carrier before you close your account and leave to come.
Some students use VOIP phone services like FaceTime, MagicJack or Skype to make phone calls to the States. High-speed or cable internet are needed as well as other equipment. If you wait to cancel your stateside number, you might be able to use the same number with one of the VOIP services here.
Here are some websites to check out for details and necessary equipment to purchase before you come: