Cheap Mobile Plans Under $20 on the Optus Network
Optus network only -- every plan below runs on Optus infrastructure. Check Optus coverage in your area before signing up.
In our database, we're comparing 19 mobile plans priced at $20 a month or less on the Optus network, from 10 providers. Prices run from $1.00 to $20.00 (more on that eye-catching $1.00 figure below), averaging $14.53, with data allowances from 5GB up to 100GB. Only 4 of the 19 keep their price with no promo increase; the other 15 start at a discounted intro price and revert to a higher regular price once the promo period ends. Billing cycles are mixed again this time -- 2 plans bill weekly (7 days), 5 bill every 28 days, and 12 bill monthly (30 days) -- so we've kept a monthly-equivalent figure alongside every price so plans on different cycles can be compared fairly.
(Yomojo, first month only)
(amaysim, 7-day)
Genuinely $20-or-under, no price hike (4 plans)
Sorted by cost per GB, lowest first. These plans cost the same now as they will on renewal.
| Provider | Plan | Data | Talk & Text | Price | Monthly Equivalent | Cost/GB | |
|---|---|---|---|---|---|---|---|
| amaysim | 7 Day SIM Only Prepaid Mobile Plan | 10GB (4G,5G) | Unlimited | $10.00 / 7 days | ≈$42.86/mo | $1.00 | View plan |
| AQUA Mobile | $20 Monthly SIM Only Plan | 20GB (4G) | Unlimited | $20.00 / 30 days | $20.00/mo | $1.00 | View plan |
| AQUA Mobile | $15 Monthly SIM Only Plan | 10GB (4G) | Unlimited | $15.00 / 30 days | $15.00/mo | $1.50 | View plan |
| Optus | Flex Plus - Weekly | 5GB (4G,5G) | Unlimited | $13.00 / 7 days | ≈$55.71/mo | $2.60 | View plan |
Starts under $20, price increases later (15 plans)
Sorted by current advertised price, lowest first. "Now" is the price you'll pay today; "Then" is the regular price it reverts to once the promo period ends.
| Provider | Plan | Data | Talk & Text | Now | Then (regular) | Monthly Equivalent | Cost/GB (now) | |
|---|---|---|---|---|---|---|---|---|
| Yomojo | Starter Prepaid | 29GB (4G) | Unlimited | $1.00 | $24.00 | $1.00/moRegular $24.00/mo | $0.03 | View plan |
| amaysim | 30GB Data Only Prepaid Mobile Plan | 30GB (4G) | N/A | $10.00 | $25.00 | ≈$10.71/moRegular ≈$26.79/mo | $0.33 | View plan |
| E.Tel | Value 25GB | 25GB (4G) | Unlimited | $10.00 | $24.90 | $10.00/moRegular $24.90/mo | $0.40 | View plan |
| amaysim | 15GB Unlimited Small SIM Only Plan | 15GB (4G,5G) | Unlimited | $11.00 | $30.00 | ≈$11.79/moRegular ≈$32.14/mo | $0.73 | View plan |
| Coles Mobile | Coles 45GB Month to Month Mobile Plan | 75GB (4G,5G) | Unlimited | $12.00 | $35.00 | $12.00/moRegular $35.00/mo | $0.16 | View plan |
| Optus | Flex Plus - 30GB Data | 50GB (4G,5G) | Unlimited | $14.00 | $40.00 | $15.00/moRegular ≈$42.86/mo | $0.28 | View plan |
| Dodo | $30 Unlimited Mobile Plan | 40GB (4G) | Unlimited | $15.00 | $30.00 | $15.00/moRegular $30.00/mo | $0.38 | View plan |
| SpinTel | 25GB SIM Only Mobile Plan | 25GB (4G,5G) | Unlimited | $15.00 | $23.00 | $15.00/moRegular $23.00/mo | $0.60 | View plan |
| Flip | 10GB Mobile Plan | 10GB (4G) | Unlimited | $15.00 | $24.90 | $15.00/moRegular $24.90/mo | $1.50 | View plan |
| Optus | Flex Plus - 35GB Data | 65GB (4G,5G) | Unlimited | $17.00 | $49.00 | ≈$18.21/moRegular $52.50/mo | $0.26 | View plan |
| amaysim | 100GB Data Only Prepaid Mobile Plan | 100GB (4G,5G) | N/A | $18.00 | $50.00 | ≈$19.29/moRegular ≈$53.57/mo | $0.18 | View plan |
| Dodo | $40 Unlimited Mobile Plan | 80GB (4G,5G) | Unlimited | $20.00 | $40.00 | $20.00/moRegular $40.00/mo | $0.25 | View plan |
| E.Tel | Value 60GB | 60GB (4G) | Unlimited | $20.00 | $38.90 | $20.00/moRegular $38.90/mo | $0.33 | View plan |
| Aussie Broadband | Value Mobile Plan | 45GB (4G,5G) | Unlimited | $20.00 | $40.00 | $20.00/moRegular $40.00/mo | $0.44 | View plan |
| E.Tel | Value 40GB | 40GB (4G) | Unlimited | $20.00 | $29.90 | $20.00/moRegular $29.90/mo | $0.50 | View plan |
Two plans in our database are data-only: amaysim's 100GB Data Only Prepaid Mobile Plan ($18.00, promo) and amaysim's 30GB Data Only Prepaid Mobile Plan ($10.00, promo). The other 17 all include unlimited talk & text.
Compare by billing cycle
Billing cycle affects how the sticker price translates to a monthly cost -- shorter cycles look cheap upfront but bill more often.
Compare by network speed
10 of the 19 plans support 5G; the rest are 4G-only.
Frequently asked questions
Prices and data allowances shown are current in our database as of August 2026 and reflect advertised carrier pricing at time of listing. Where a plan has an introductory promo, we show both the current and regular price so you can see the true long-term cost. Monthly-equivalent figures are calculated as price × (30 ÷ billing days) and are provided for comparison purposes only -- they do not represent an actual monthly billing amount for plans that don't bill monthly. Plans, prices and inclusions change frequently, and details are entered into our database manually so errors are possible -- we do not guarantee the accuracy of any price, allowance, or other detail shown. Always confirm the final price, billing cycle, and all plan information directly with the carrier before signing up.