I’ve reviewed Pfingo and used Skype Pro when calling within Canada and the US. It’s time I shared how I call Singapore from Shanghai.
Cheapest:
Pfingo. Even though my free unlimited calls have expired, calls to Singapore are only S$0.01 per minute, while SMSes are S$0.05 for local SMS and 10 cents for overseas SMS.
(Using Skype sets me back for calls at more than S$0.03/min, and SMSes more than $0.15/SMS)
Thanks to Pfingo’s referral program, I have sufficient credits to last me for quite a while. 
However, since it is a VOIP service you’ll need an internet connection.
Most Convenient:
IP Card + Mobile Phone. The cheapest IP card I’ve found here (17900, China Telecom) is one that charges 0.3yuan/min for calls to Singapore. However, cards valued at 100RMB are being sold for 35RMB. Therefore, combined with my current prepaid plan (16RMB/S$3.20 a month) on my mobile phone (calls charged at 0.13yuan/min), calling Singapore would cost me approximately 0.25yuan/min, which is S$0.05/min.
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The best solution might still be getting the party in Singapore to call you, while you enjoy free incoming calls on your mobile phone (with prepaid plan at 16RMB/S$3.20 a month) or fixed line. 
