You mentioned you want to keep a number, so I assume you are planning to MNP To Digi online (so you will get a free McD burger!)... If you choose Digi Best (Version 2017 only),
[1] Free 1GB high speed internet everyday from 12am-8am. If you don't buy high speed internet, you still can use basic internet (capped at 500MB per calendar month)
[2] If you make IDD calls (10 countries only) >RM1 in a day (I called China 13 times in early morning to spend RM1.04, the cheapest possibility), you get another 1GB high speed internet to be used till end of the day (11:59pm).
[3] You top up RM30/50/100 to get 30/50/120 days active period, and RM30/50/100 (+bonus) credit.
[4] Use RM108 credit (not top up) for SLL 365 days. You can find this in the menu only when your credit >RM108.
[5] So when you activate the SIM card, you buy RM100 to get 120days active period. At 121th day, you top up RM30 to get +30 days active period. Then at 151th day, you can choose SLL365@RM108. provided you don't spend your credit all the time. It is wasted if you top up RM100+ and immediately go fo SLL365.
[6] Wifi Hotspot is possible, subject to the internet quota you have (1GB from 12am-8am etc). I use phone-to-phone, I haven't tried using 3G/LTE modem.
[7] You can use M2U(Wednesday only)/MyDigi to get bonus but the bonus is valid for 24 hours (M2U-Wed), 72 hours (MyDigi). T&C apply.
[8] Sometime Lazada may give out some discount codes, you can top up at Lazada-Wisepay at discounted price, eg I spent RM80.10 to top up RM100 last week.

Haha Call +864008208878 HSBC China Phone Banking. 8 sen per 30 seconds.
Disconnect the call once your call is connected. Do it 13 times to achieve >RM1.
At 7th call, you will get a SMS from Digi. You will get another SMS after 13th call. Redeem the free 1GB at *888*1#.
https://personal.hsbc.com.cn/en-cn/ways-to-bank/telephone/

Also don't forget to set special call rates for 10 Digi numbers + 10 non-Digi numbers.
Use whatsapp or wechat to call if possible.