This is ridiculously overpriced.
Tip: If you’re visiting another country, even say for only a few days, get a local sim from them. Most sim cards already come with unlimited data out of the box for a lot less price than P500 a day. Or even if you have to top-up, still going to be cheaper.

Did this both in the UK and in Hong Kong.
In UK, I got a sim pack from ThreeUK which offered unlimited data for 30 days, 2000 minutes of all, and 2000 texts
All for £ 20 (approx. P 1,500)
Imagine, this is for 30 days! For the same amount, you only get 3 days with smart roaming. And definitely no thousands of free calls and texts.
In Hong Kong, I got a PCCW-HK Tourist sim, which was good for 5 days. Does not offer unlimited data, though. I think I had about 3GB of data (Uhm, not really sure?? But point is, still cheaper than 500/day to update and check-in to places), which is just about enough for a few days stay.
If you don't already know, Facebook browsing, and tweeting is not going to reach up to a gigabyte in 5 days. I was using data mostly for the maps, and even the maps will not max out to more than your limit for a few days. You can top-up for unli data if you really want to. You can check out their site but I'm betting my bottom dollar it's still going to cost less that Smart's roaming rate. (Goodness, who knows how fast and reliable this data roaming is?)

For your reference:
Three UK Pay As You Go SIM (Unlimited data for 30 days)
Heathrow Terminal, London (Vending machine in exit doors going to parking lot) - £20

Hong Kong Tourist Sim Card
7-eleven , Ground Floor, Hong Kong Int'l Airport - HKD 59

Let me know if you have questions and I'd be very happy to help!