Sim card for overseas voice calls and 3G for a month

Hello everyone, it is my first time posting in the Malaysia forum. I'm Ham, just a student from Switzerland who likes travelling. Nice to meet you all. :]

I'm here because I have question about the SIM cards available for travellers in Malaysia.

I am going there for a month with my Malaysian friend (she is Malayisan but was born and raised in Switzerland, hence she cannot help me much), and I will travel in various places (still not precisely planned) such as Kuala Lumpur, Penang, Melacca, Johor, Redang or Tioman Island and Sarawak. I use an iPhone 5S which is unlocked.

I've been looking through google for informations but all answers and questions were outdated. I think that things have changed since then, that's why I'm trying to ask here. (Indeed, what I've read for Vietnam was not applicable anymore by the year I went over there…) Plus, I couldn't really understand the Malaysian telecommunications carriers' sites.

Being there for exactly one month, I would like to be able to call home in Switzerland, sometimes, with an interesting cost rate for a reliable connection (it cannot be super  expensive, can it?) and to surf on the net (mostly social networks/instant chat for instance and perhaps a bit of google map) from time to time, in different places out of the cities. No super speedy connection is needed for those activities; as long as it works and covers a large territory, it's fine. No need for 5GB (omg) of data as well, 1GB for the month is already way enough.

I've seen that many people talk about Celcom that has good staff and services, Maxis as well because they have shops almost everywhere, and DiGi (but their covered areas are restricted and their 3G does not always work well, according to a few travellers).

What are the xpax SIM cards? Are they easy to find, to buy, and to use? What would you guys recommend me to get for a month of holiday in Malaysia?

Thanks in advance for any help!