A commercial mobile telecommunications service typically utilises a cellular network structure in which users communicate using mobile station terminal equipment (mobile handsets) and base transceiver stations located in the cells. In a modern system such as the GSM system (global system for mobile telecommunications), each mobile handset contains a subscriber identity module (SIM). The SIM is a smart card, and has a computer memory chip permanently installed thereupon. The SIM is a crucial element of the GSM system, in that it contains user specific information such as the identity of the user (the telephone number of the user), information to ensure that calls are billed to the user, information to enable the user identity to be verified by the network, information to provide security by voice encryption, and telephone numbers saved as short dial codes that are specific to the user. The SIM can also be used to contain other information defined by the network. In fact, the SIM is the only part of a mobile telephone which is truly personal to the user. Conventionally, a SIM card is installed semi-permanently within the handset of a mobile'phone.

A SIM card is usually in the form of either a credit-card size card (measuring approximately 85mm x 54mm x 0.8mm), or a smaller card (measuring approximately 25mm x 15mm x 0.8mm). In the latter case, the SIM card has a chamfered corner to ensure correct insertion of the card by engagement with a complementary feature formed on a SIM card holder inside a mobile'phone handset.

A PC card (previously known as a PCMCIA card) is a peripheral module which is commonly used in conjunction with a host device such as a personal computer (PC). In its most common form, a PC card comprises a printed circuit board (PCB) located in a slim casing, the PC card being pluggable into a peripheral port of a PC or other host

device in order to perform a particular function. Thus, a wireless PC card might include a GSM transceiver for allowing an associated host device such as a PC to access the GSM wireless communications network. A PC card generally comprises a plurality of electronic components in the form of sub-circuits or sub-modules.

Whatever form it takes, a PC card has a small active area (for example a 68-way connector) provided on one face of the card for connection with contacting elements of the PC card circuit board, and means (for example a 15-way and RF connector) provided on the opposite face for connection with an external device.

Typically, the SIM card of a mobile'phone handset is inserted into the handset, and retained therein by some electro-mechanical connection within the housing of the handset. One of the features of a SIM card is that it is transferable between host devices. Thus, a SIM card can be transferred between different GSM handsets and other GSM products, thereby transferring account information from one host device to another, and allowing charge usage of multiple products to be entered on the one account. In particular, a SIM card can be used with a wireless PC card, in which case the SIM card insertion function is difficult to implement in a reliable manner.

The aim of the invention is to provide a PC card which facilitates reliable insertion of a SIM card.

The present invention provides an electronic module for positioning within a host device, the electronic module comprising a casing, electronic circuitry within the casing, an aperture positioned in a wall at one end of the casing, the aperture being sized to receive an auxiliary electronic device, and contact means associated with the electronic circuitry within the electronic module being arranged to make electrical contact with contact means formed on the auxiliary device, wherein the module is provided with guide means for guiding the auxiliary electronic device into a position in which its contact means make electrical contact with the contact means of the electronic circuitry, the guide means being such as to prevent insertion of the auxiliary electronic device into said position in any orientation than a predetermined orientation.

In a preferred embodiment, the module is a PC card which is adapted for insertion into the host device via an entry aperture in a casing of the host device, and said casing wall is that wall of the PC card which, when the PC card is positioned within the PC, is remote from said entry aperture.

Advantageously, the module further comprises connection means for electrically connecting the electronic circuitry to electronic circuit means within the host device.

Preferably, said connection means is positioned in said casing wall, and the aperture in said casing wall is adjacent to the connection means.

Preferably, a a SIM card constitutes the auxiliary electronic device. The SIM card may be generally rectangular with one of its corners chamfered, and the guide means may be provided with a mechanical feature that complements said chamfered corner.

The invention will now be described in greater detail, by way of example, with reference to the drawings in which :- Figure 1 is a plan view of a PC card constructed in accordance with the invention and an associated SIM card; Figure 2 is a schematic representation of an associated host PC; and Figure 3 is a side elevation of the PC card and associated SIM card.

Referring to the drawings, Figure 1 shows a PC card 1 having a casing 2 which houses a PCB (not shown) and a plurality of electronic components (not shown). The casing 2 is provided with a 68-way connector 3 (see Figure 3) in its rear face 2a, that is that face of the PC card casing which, in use, is first inserted into a a docking area 4a in an associated host PC 4 (see Figure 2) in the direction of the arrow A. An aperture 2b is provided in the rear face 2a, the aperture being sized to receive a SIM card 5 which measures approximately 25mm x 15mm x 0.8 mm. The aperture 2b is formed as a cut-away in the casing rear face 2a, the cut-away being positioned above the connector body (not shown) of the 68-way connector 3. As with prior art arrangements, the SIM card 5 is retained within the PC card 1 by an electro-mechanical connection (not shown) known per se.

As shown in Figure 1, the SIM card 5 is formed with a chamfered corner 5a. A keyed guide 6 provided within the PC card 1 is formed with a chamfered guide surface 6a which complements the chamfered corner 5a of the SIM card 5. This ensures that, when the SIM card 5 is inserted into the aperture 2b with the chamfered corner Sa at the leading edge and on the left (as viewed in the direction of insertion indicated by the arrow B), the chamfered corner contacts the chamfered guide surface 6a to guide the contacts (not shown) on the SIM card into proper contact with complementary contacts (not shown) provided inside the PC card 1.

The configuration of the PC card keyed guide 6 described above ensures that a SIM card can only be inserted in a correct manner, thereby eliminating the need for the PC card to incorporate short circuit protection. Moreover, as the entry aperture for the SIM card is positioned at the 68-way connector end of the PC card, the latter cannot be fully inserted into an associated host device unless the SIM card is fully and correctly inserted, that is to say it does not protrude from the aperture. Another advantage is that the SIM card is fitted into the rear edge of the PC card casework immediately over the 68-way connector, thereby making good use of the available space within the PC card.