Internet and phone service in Haikou

As far as I know, most the star-hotels, restaurants, cafes and many shops are available for Wifi in that city. So you can ask the staff to confirm whether their places have wifi. The provide wifi for free.
There are many cell phone shopps in the city. It is suggested to go to China Telecom and China Unicom shops to buy cell phones.

I won't be in a hotel, as I am staying for a long time. I have a cell phone but would need phone service. I used sim card phone in Thailand that I could buy minutes at the 7-11.

If you plan to live in aparment and want to connect the internet in the apartment, it is suggested to go to the local China Telecom or China Uncom company where you cannot only get sim card for your cellphones but also the internet service.