Hi,
Dummy issue is a tough one. I don't like seeing babies/children with dummies.
That said we ended up giving DD a dummy when she was 6 weeks old. It was after 2 of my friends admitted that they still sucked their thumbs (both mid-thirties) every night (or when relaxing or watching tv) despite many attempts to stop. Neither were given dummies as babies and with the current SIDS advice of dummies being helpful, we gave one to DD.
She now 12 months and from the very beginning she's only had it for sleep time and still only has it for her nap and bedtime.
In many respects its excellent. She's a dream sleeper and settles so well and loves going to bed. The dummies are tied her comforter.
We've never had any sleep issues with DD at all and from she was 6 months and I stopped BFing and stopped milk during the night, she does not wake and she does not call for us.
If you can tie the dummies to a comforter, your LO can always find them during the night and it prevents them falling out of the cot etc. And your LO can settle him/herself again without you having to get up.
We're getting towards the time where DD will have to give up her dummies. I am in the process of weaning her off the bottle for milk so dummies have a reprieve until that its sorted and has settled down.
I don't think you need to take the comfort the dummy provides away from a 4 month old. They're only small and clearly enjoy the comfort from the dummy. You may also save yourself a lot of sleep issues by keeping the dummy.
There will inevitably be tears when the dummy goes, whatever age the baby is, but I'd rather DD was old enough to understand most of the explanation given (the smaller babies need it, they're all broken etc etc), than have a small one howl and howl for comfort when they're too little to understand why.