I have a post up on Japan Mobile Tech on how I cut my smartphone cost to less than 1/3 of before — from 7500 yen to 2000 yen — while keeping the same service on the same physical network.
The trick? Split
voice and data into separate subscriptions. I got myself a brand-new flip-phone as my
actual phone, and changed my Docomo account to a FOMA voice-only account. 1050 yen a month in total.
Then I got a data-only SIM from IIJmio for my smartphone. That's 935 yen a month for 3GB. We can keep our free family calls on Docomo, while paying only a fraction of the data cost. And IIJmio uses the same physical network as Docomo, so there's no practical difference in reception or data speeds.
In all, I will save about 100 000 yen over the next two years. Not bad for a bit of creative contract juggling.