Iridium is a truly global system, covering all the earth's surface and airways. The service has been banned for political reasons in three countries, North Korea, Poland and Sri Lanka, but otherwise the network has 100% coverage of the surface, including poles, airways, oceans etc, as long as you can see a reasonable expanse of open sky. Like for Globalstar, the system is a low earth orbit one, with 66 satellites (plus spares) orbiting at about 480 miles above the earth's surface.

Unlike for Globalstar, calls and other traffic are passed on radio links between the satellites, and are linked to the ground only at a couple of earth stations in the USA. This enables Iridium to Iridium calls to be routed over satellite only, it also means that the system operates as a global one as opposed to multi-region, all calls (other than Iridium-Iridium) are charged at the same flat rate which makes managing the cost of your usage much easier. It also means that the system does not rely on having an earth station located in that particular part of the world to offer coverage - resulting in coverage in the remotest areas including the poles.

Following the financial re-structuring / sale of the original company in 2002, Iridium no longer offers dual mode handsets or roaming on terrestrial networks. It's a standalone satellite network, meaning that, as well as having a handset, you must have either a pay monthly or pay-as-you-go Iridium SIM card to use with your phone. Phone numbers begin +8816 or +8817 and, as for Globalstar and Thuraya numbers, can be expensive to call from landline or conventional mobile phones. Iridium does however have an Email to SMS gateway (to/from handset) enabling people to send messages to the handset from the internet. This does not currently work in either direction between GSM and Iridium handsets (tested to/from Vodafone UK only).

Iridium phones used to be made by Motorola, they are now made by a third party especially for Iridium, but the menu structure is still based on Motorola's and is particularly familiar to anyone who has used a Motorola cellular phone in the past.

The current phone (9505A) is less long than the Globalstar (Telit 550), while still significantly larger than a conventional mobile phone, but still an amazing compact unit that will fit into a large coat pocket. Build quality is good.

Upon power on, the phone logs onto the network very quickly, within a few seconds, faster than for the other two networks. Call clarity is acceptable and perfectly usable but it is apparent that there is significant compression on the line (more so than for Globalstar in my opinion). When returning to coverage, phone quickly logs back on network without fuss - in my experience much better at this than the other two nets.

Good points

- the truly global coverage - aside from the three banned countries, no need to look at coverage maps again. Quick registration and re-registration to network, little waiting around. For most users, flat rate billing worldwide provides clarity over call charges - outgoing rates from handset are often better than for GSM roaming.

Bad points

- no roaming with GSM networks available. Some users report dropouts on data calls, which can be inconvenient as the call has to be re-initiated (I did not test the data feature).

OVERALL - surveying all three networks, overall Iridium was my favourite as it had the widest possible coverage and worked well. While I have encountered no problems with the Iridium handset, the Thuraya handset was my favourite of the different satellite handsets, being the most compact.

Pictured: close-up of handset while connected (five signal bars, clock, full battery indication), overall view of handset while connected, back of handset with antenna up, and then stowed, part of Iridium kit with leather case, spare battery, mains charger.

NB diskette pictured is not part of hire kit, but there to give an idea of scale.