Keeping Your Overseas Number Alive: Carrier Rules & Minimum Costs
giffgaff needs one SMS every six months; Ultra Mobile needs a monthly plan. Understand carrier retention rules to avoid losing your number.
Numbers get recycled only when inactive for too long. Every carrier defines activity differently; once you know the rules, retention cost drops dramatically.
UK giffgaff: cheapest to keep
One SMS or call every 6 months keeps the number, with no monthly fee. Nearly zero cost for SMS-only use.
US Ultra Mobile / Mint Mobile: keep a plan active
US prepaid carriers require an active plan. Ultra Mobile’s PayGo plan starts at $3/month and is the go-to for keeping a US number long-term.
HK CMHK / csl: validity-based top-ups
HK prepaid cards run on stored-value validity. Each top-up extends the window; the minimum denomination before expiry keeps it alive for tens of HKD per year.
Pro tips
Set a calendar reminder one week before each deadline, or use our top-up service to auto-renew so you never lose a number.
