transpac

Keeping a SIM active during infrequent visits creates challenges. And Skype (assuming VoIP) can use a great deal of one's allotment of data.

Without understanding the different locations you/wife might travel to in Thailand I might continue to recommend a TrueMove H nano-SIM for the factory/carrier unlocked iPhone 5, as they have the most geographical coverage, and the least utilized network - this is actually a CAT network and TrueMove H is a MVNO/reseller. One potential downside is the TrueMove's traditional GSM network, onto which TrueMove H customers roam when outside of coverage, is due to close on Sep. 15, 2013, also leaving 18 millions subscribers without service. Whether this ultimately happens remains to be seen, on 16 Sep.

DTAC/Happy also remains a recommended option, maybe nearly equal to TrueMove H save 3G coverage. DTAC/Happy do offer 3G coverage in all of the provincial capitals, and larger cities and tourist destinations.

Perhaps the easiest way to keep a SIM active would be to leave it with family/friends and ask them to maintain it. In the case of a TrueMove H SIM this simply requires originating/receiving a 5 second voice call once every 60 days - with this activity the expiration is automatically extended 60 days. With the Krong Kra Pun DTAC/Happy SIM, the same activity extends the validity 43 days. Or you could leave some money here and ask people to top it up. You could even enable international roaming, and top-up as required in your home country, assuming GSM coverage. This would work in the U.S., for example with T-Mo or AT&T.

With Skype VoIP calls you can consume a lot of bandwidth, using up your 3G allowance quickly, so maybe best to use WiFi for Skype calls, or even just one of the low-cost long distance prefixes like 009.