I installed it on my ipad2 and ipod 4g ( Look Mana, i turned ipod to iphone4 lol

) since the announcement date and tested many calls. Below is my review.
1. Call quality was choppy and slightly delayed on streamyx 1mb line. I can hear the voice clearly from the person i called who was using standard Malaysian mobile and fixed line but he can't really comprehend my breaking conversation. Often times I need to repeat 2 to 3 times to make myself clear. Thus the 9 sen per min call rates needs to x 2 times too sometimes

.
2. Almost the same features as Skype pay as you go plan but YES offers cheaper call rate for Malaysia mobile lines. Comparison between Skype mobile and Yes iOS as below.
2.1 The call rates for skype r approx 8sen for fixed line and 21sen for mobile. A one time connection fee of 13.5sen applies. YES win in call rates
2.2 Skype credit has no expiry if you use it once every 180days. YES need minimum usage of RM30/mth. Skype win in credit validity.
2.3 Skype account never self terminated due to inactivity, YES will, if we fail to top up RM30 every month.
2.4 Skype doesn't provide Malaysian local number, YES gives 018 number. YES win in incoming call capability.
2.5 Skype is multi platforms ie iOS, Android, Symbian, Window whereas YES only iOS and Window.
2.6 Skype needs cerdit card and debit card to buy whereas YES can accept cash, M2U, credit card, debit card.
3. For most users, one can hardly fully utilized the 018 incoming call phone number due to the fact that we can't online 24/7.
4. Good for calling home from overseas provided that you have Internet access.
5. I'm not very optimistic to use it as an incoming call option when traveling overseas simply because who and when will call me at what time is beyond my control and i can't always be in the wifi range to standby. Also for the fact that most of my customers will continue to call me at my primary phone number.
The conclusion. Well, the biggest drawback is the rm30 minimum monthly usage, otherwise it can be the good alternative to Skype pay as you go or a cheaper alternative for outgoing voice call and sms.
If you are an exiting YES wimax user for its mobile internet service (me too), by all means why not ?