Last updated: Friday 18 September 2026 (Europe/London).
Next update: when iD Mobile or Talkmobile reprint 100–150GB SIM ladders on their own shops.
By: Switch Editorial Team, Switch Squid Ltd
As of 18 September 2026, the cleanest retailer-verified 120GB SIM-only cash lead we opened is iD Mobile’s 120GB plan at £12 a month on idmobile.co.uk (£144 over 12 months), with unlimited UK minutes and texts and no annual mid-contract price rise on the listed 1-month SKU. Talkmobile does not sell an exact 120GB tier today — its nearest cash neighbours are 100GB and 150GB half-price 12-month promos. SMARTY jumps from 100GB (£12) to 150GB (£15) with no 120GB rung.
I am Switch. This guide answers 120GB SIM only deals UK for people who want roughly four months of heavy phone data without jumping to unlimited. Soft context sits on the mobile hub; primary Get deal buttons use Nest Awin deepLinks (publisher 911601), destination-verified to a live iD basket — never an own-hub Compare as the money button.
Get deal — iD 120GB SIM-only (live Awin) →
Who 120GB is actually for
120GB sits in the awkward middle: too much for light WhatsApp users, shy of “never check the meter” unlimited. In practice it suits mixed households that hotspot a laptop a few evenings a week, short-form video every day, and the odd weekend of maps-heavy travel — without paying the Unlimited premium on SMARTY (£20) or iD’s unlimited rungs.
If you routinely burn more than ~100GB on the phone alone, price the Unlimited tier on the same network before you congratulate yourself on a 120GB “bargain”. If you barely crack 40GB, SMARTY’s 40GB at £10 or Talkmobile’s lower rungs will usually beat 120GB on 12-month cash.
Verified cash table (18 Sep 2026)
| Retailer / product | Data | Monthly / promo cash | Term | 12-month cash | Network | Source |
|---|---|---|---|---|---|---|
| iD Mobile 120GB | 120GB | £12/mo | 1-month listed | £144 | Three | idmobile.co.uk |
| Talkmobile 100GB promo | 100GB | £4.98 for 3m then £9.95 from 17 Dec 2026 | 12 months | ~£104.79 (3×£4.98 + 9×£9.95) | Vodafone | talkmobile.co.uk |
| Talkmobile 150GB promo | 150GB | £5.97 for 3m then £11.95 from 17 Dec 2026 | 12 months | ~£125.46 | Vodafone | talkmobile.co.uk |
| Talkmobile 100GB rolling | 100GB | £9.95/mo | 30 days | £119.40 | Vodafone | talkmobile.co.uk |
| SMARTY 100GB | 100GB | £12/mo | Rolling | £144 | Three | smarty.co.uk |
| SMARTY 150GB | 150GB | £15/mo | Rolling | £180 | Three | smarty.co.uk |
| SMARTY Unlimited | Unlimited | £20/mo | Rolling | £240 | Three | smarty.co.uk |
Opened on retailer.com 18 September 2026. Comparison-site exclusives (e.g. iD £2.25 intro tiles on uSwitch) are omitted until the same cash appears on the retailer’s own checkout. O2 Nest 120GB affiliate rows existed but destination-verified into an O2 waiting room — not used as a primary CTA.
Get deal — open live iD 120GB basket →
How we ranked 12-month cash
For rolling plans we multiply the published monthly fee by 12. For Talkmobile’s half-price intros we use the retailer’s own “then £X from [date]” wording rather than inventing a blended APR. That is why Talkmobile’s 100GB promo can undercut iD’s 120GB on cash while delivering 20GB less data — decide whether you need the extra 20GB more than you need ~£39 back in the year.
iD’s listed 120GB at £12 with no annual price rises on the shop copy is the cleanest like-for-like 120GB line. Talkmobile wins the near-tier cash contest if you accept 100GB or stretch to 150GB and stay for the full 12 months after the intro.
Roaming, 5G and credit checks
iD markets Take Your Tariff Abroad style roaming in 50+ destinations on its SIM-only pages — always re-read the plan’s fair-use GB before a long trip. SMARTY and Talkmobile publish their own EU/roaming footnotes; do not assume phone-plan roaming equals data-SIM roaming.
5G is included on the iD and SMARTY rungs above where the mast and handset support it. Coverage still follows the host network (Three for iD/SMARTY; Vodafone for Talkmobile).
Rolling MVNO plans often skip hard credit checks; 12-month contracts may not. If you need approval-free switching, prefer the 1-month iD/SMARTY path and keep a PAC ready.
Switching with a PAC
Text PAC to 65075 from the old SIM, then give the code and number to iD/Talkmobile/SMARTY during checkout. Porting usually completes in one working day once the gaining provider submits it. Keep the old SIM until the number lands so you do not lose inbound SMS mid-switch.
What we did not put in the cash lead
Three’s own shop soft-blocked our crawler behind a queue token today, so we do not invent a Three.co.uk 120GB monthly figure even though third-party tiles float ~£12. Lebara and giffgaff did not show a clear public 120GB ladder in this research window. VOXI’s published plans centre on 20GB/100GB social-data bundles rather than a plain 120GB phone SIM.
FAQ
What is the cheapest 120GB SIM only deal in the UK right now?
On retailer.com as of 18 September 2026, iD Mobile’s 120GB at £12/month (£144/year) is the cleanest exact-120GB lead we verified. Near-tier Talkmobile 100GB promos can be cheaper on 12-month cash if you accept less data.
Is 120GB enough for hotspotting?
For light laptop tether evenings, yes. For daily 4K streaming hotspot, price Unlimited instead — 120GB disappears faster than people expect once two devices share it.
Does iD use Three’s network?
Yes. iD Mobile is an MVNO on Three’s radio. Coverage and 5G availability follow Three’s mast map, not a separate iD radio layer.
Why ignore uSwitch’s £2.25 iD promo?
SwitchSquid only ranks cash that appears on the retailer’s own site. Comparison exclusives that vanish at retailer checkout are dropped under our retailer-verified rule.
SMARTY has no 120GB — what should I buy?
Choose 100GB at £12 if you are under ~90GB usage, or 150GB at £15 if you regularly crest 110GB. Jumping to Unlimited at £20 only pays when you hate metering.
Can I keep my number?
Yes — request a PAC and port in. The gaining provider triggers the move; you should not need to call the losing provider to “cancel first” for a standard UK mobile PAC port.
Are these affiliate links?
Yes. Get deal buttons use Awin pclick URLs with publisher id 911601. They were destination-verified to a live iD Mobile basket before publish.
Get deal — iD 120GB via Awin 911601 →
Worked 12-month examples (honest arithmetic)
Take a London-based hybrid worker who averages 95–110GB on the phone and hotspots a laptop two evenings a week. On iD’s 120GB at £12 they finish the year at £144 if the monthly fee stays put. On Talkmobile’s 100GB promo the blended year is about £104.79 — cheaper cash, but a 20GB thinner ceiling that forces a mid-year upgrade if usage creeps. On SMARTY 150GB at £15 the year is £180: more headroom than iD 120GB, £36 more cash.
Now flip the profile to a student who streams on mobile every night and hits 140GB. iD 120GB becomes a false economy — overage or an emergency Unlimited jump mid-contract erases the “deal”. SMARTY Unlimited at £20 (£240/year) or iD’s unlimited rung (check live shop) is the honest product. This is why we refuse to crown a single UK winner without a usage sentence under the H1.
eSIM vs physical SIM for 120GB plans
iD and SMARTY both push eSIM on many handsets. eSIM ports are usually faster for PAC moves because there is no Royal Mail delay, but dual-SIM travellers should confirm the handset can hold the new eSIM beside a foreign travel SIM. Physical SIMs still matter for older MiFi hotspots that lack eSIM profiles — if your hotspot is data-only hardware, confirm the 120GB phone SIM’s APN works before you bin the old card.
Activation tips we keep repeating after messy customer emails: leave the old SIM in until the port completes; do not delete the eSIM profile until data flows; screenshot the order confirmation with the Awin click ID if you ever need affiliate support.
Annual price rises — read the small print once
Big-four style mid-contract rises (often CPI or a fixed percentage each April) still appear on many 12–24 month contracts. iD’s shop copy for the listed 120GB 1-month plan emphasises no annual price rises; Talkmobile and SMARTY MVNO plans frequently market the same. That marketing is why MVNOs dominate this cash table. Re-read the order summary on the day you buy — publishers and retailers change footnotes without blogging about it.
Internal links for shoppers who are not on a 120GB brief
If you are closer to a lighter allowance, our recent data only SIM UK guide covers tablet/MiFi cash. For longer locks, the 24-month SIM only deals UK page (where live) explains when a longer term is worth the discount. Soft hub: mobile deals.
Get deal — iD 120GB live basket →
Family plans and secondary SIMs
120GB is usually a single-SIM story. If two teens share a hotspot from one handset, you will burn the allowance faster than the cash table suggests. In that case either buy Unlimited or give each person their own cheaper 40–100GB SIM. Multi-SIM “family” discounts on big networks sometimes look neat until mid-contract rises hit every line — MVNO singles remain easier to cancel line-by-line.
Secondary SIMs in watches and tablets should not silently sit on the same 120GB pool unless the retailer says so. Wearable plans are usually separate products; check before you assume the watch “just shares”.
Sources: idmobile.co.uk/sim-only-deals, talkmobile.co.uk/sim-only-deals, smarty.co.uk/sim-only — opened 18 Sep 2026.
