Friendi has the same sms rate as U Mobile(8cent, as it is using U Mobile's network), but validity is not an issue as with every sms/call/reload you'll get 60 days validity(which is literally unlimited validity)

http://www.friendimobile.my/prepaid-mobile#domestic-rates

Well, you're using U Mobile right, why ask me Anyway, I literally have three telco's sim(UM, DiGi, Celcom, Maxis(through U Mobile)), so U Mobile does not really have a very limited coverage actually, but it does has its blind spots(but every other telco has it too, it all depends on your area, see which one is better there). If you don't data on that sim, you can put it to run on 2g only, so it will use Maxis's network for calls/sms/data, I believe Maxis should be good enough for you, no? if Maxis no signal can put back U Mobile maybe got signal, not bad no?

If you need data + sms, then Altel would be a better choice(its rm28 internet package has 1gb data for 3 months, extending your credit validity to 3 months from the day of subscription as well), however for your use case, if you don't need that then friendi would be the better choice.

That aside, since the 1gb is free for power prepaid, the remaining 30 ringgit tak cukup ka for your calls + heavy sms