Looking for a 3G wifi broadband plan? It's a byzantine task trying to compare Irish operators' pricing and data plans. So here's a chart comparing Irish operators' (i) prepay wifi dongle plans and (ii) billpay wifi dongle plans.
Mobile operators sell two kinds of mobile broadband devices. One is a stick that slots into your computer's USB port. The other is an oval dongle (see picture above) that generates its own wifi signal. Up to five devices (laptops, iPads, smartphones, desktops) can use it at the same time. This is the one I'm focusing on in this post.
Note: this is aimed mainly at novices and beginners. In other words, where there has been a choice between various 30-day access packages, I've chosen the cheapest one available, based on an assumption that novices are less likely to be power-users. I've added in the higher data options in the fine print section below each table.
(i) PREPAY WIFI DONGLE BROADBAND PLANS
Operator 3 O2 Voda Meteor Emobile
Dongle price: €70 €60 €60 €70* €60
1 day access €5 €4 €3 €3 €3
1 week access €10 -- €10 -- --
1 month access €15 €20 €20 €20 --
Out-of-bundle MB €1 €0.02* €0.19 €0.02* €0.02
(ii) BILLPAY WIFI DONGLE BROADBAND PLANS
Operator 3 O2 Voda Meteor Emobile
Dongle price: €10 €30 €40* €40 €40
1GB €10 -- -- -- --
5GB -- -- -- €17 --
10GB -- -- €20 €20 €20
15GB €20 €20 €25* -- --
20GB -- -- -- €25 --
30GB €26* -- -- -- --
Out-of-bundle MB €0.05 €0.02 €0.02 €0.02 €0.02
* Now here's the fine print (including data caps) on PREPAY plans:
3 Ireland: 1 day access up to 500MB. 1 week access up to 2GB. 1 month access up to 1GB. HIgher-priced 1 month packages are also available for up to 20GB (€35). 3 also has a current offer where pre-pay broadband dongle comes with 1GB of free data pre-authorised. However, wifi dongle is currently out of stock. O2: 1 day access up to 500MB. 1 month access up to 5GB. Out-of-bundle charge of 2 cents per megabyte applies until the session is over and then you must take out a new full-price top-up. O2 also offers a "free 24 hour pass" when you initially sign up. O2 also has a special dangle purchase price of €80 with €40 credit. Vodafone: 1 day access up to 500MB. I week access up to 2GB. 1 month access up to 5GB. Add-on data allowances of 500MB (€3), 2GB (€10) and 5GB (€20) are available on prepay plans. Meteor: dongle is €60 if purchased online. 1 day access up to 500MB. 1 month access up to 7.5GB. Free access to Eircom public wifi hotpots with subscriptions. Meteor's high speed broadband access coverage is limited to large urban areas. Emobile: 1 day access up to 500MB. 1 month access up to 7.5GB.
* And here's the fine print on BILLPAY plans:
3: 30GB tariff of €26.24 is a promotional tariff, ends Feb 28th. O2: purchase price is based on 18 month contract. For 12 month contract, €50 purchase price applies. For 6 month contract, €60 purchase price applies. Vodafone: 15GB (€25) plan also gives higher speed, free modem ('up to' 14.4Mbs download) on 18-month plan. A reduced rate of €17 per month is available to Vodafone bill pay phone customers. Meteor: Prices based on 12-month contracts. For 18-month contact, 20GB product falls to €20 per month. Wifi dongle costs €20 extra if bought with 5GB or 10GB plans. Free access to Eircom public wifi hotpots with subscriptions. Emobile: 12-month contract applies

So which one do I use?
I've used wifi dongles from 3, O2 and Meteor, on and off. Of these, I've found 3's dongle probably to be the fastest and the widest in reach. Meteor gives a great perk in the form of free wifi at Eircom public hotspots, but its own high speed 3.5G coverage is far more limited than its rivals. I only recently started using O2's Hotspot wifi dongle and have found it to be a reasonably decent service.
OTHER ISSUES/QUESTIONS
1. How wifi broadband dongles work with your computer/tablet/smartphone: when you turn the dongle on, it emits a wifi signal (based on the sim card housed within it). You will see the dongle's wifi signature in your device's wifi detector. Simply choose it, enter the given password and you're connected. Up to five devices can access this wifi signal at the same time. The dongles are rechargeable: you will get between 3 and 5 hours use from a single charge, generally.
2. Where do they work? Anywhere that you find a 3G mobile phone signal (which is all urban areas and most towns or large villages). I have used dongles with little problem in remote West Cork (Beara peninsula) and rural Mayo (Erris and Belmullet).
3. Do they suffer form the same constrictions as mobile phone signals? Yes. So for example, they work less well in basements or deep inside a large building (unless there are extra transmitters in the building, such as a shopping centre). So if you normally have difficulty picking up a strong mobile phone signal in your home or your office, you will also have difficulty using one of these devices for your internet access.
4. What speed to they connect at? Generally 'up to' 7.2Mbs (download) and 'up to' 5Mbs (upload). (Some connect 'up to' 14.4Mbs.) In practice, it's about half that speed in urban areas and can be as little as a tenth of the advertised speed.
In general, I've been pretty happy with 3G broadband, mainly because I move about a lot. But it may or may not be the right service for you.