Your phone needs to be unlocked from its current network
SIMs will be quite easy to find in plenty of shops, like here
There are 3 main networks and a number of virtual providers including supermarkets. You can compare them at
http://www.prepaidgsm.net/en/france.htmlAs you'll see, the ordinary tariffs aren't that good, but if you look more deeply on the network's own sites you'll find some useful add-ons, e.g. Orange illimité inclusive packages, or SFR has an option with a 30 cent charge for up to an hour to landlines and SFR. This would be good with a local access number for a calling card or similar arrangement to call back to the UK.
Another way to make cheaper calls would be to use it with a callback service, which sets up 2 calls, the first to your phone, then to the destination
French SIMs tend to be short-lived if not regularly topped up, so your choice might also depend if this is for a one-off visit or at regular intervals
Another possibility, and especially if you'll visit other countries as well, is that there are several global roaming SIM cards with free incoming calls in many countries, and outgoing rates from about 20p a minute. Some of these have Isle of Man or Jersey numbers, which come from some but not all UK network's inclusive minutes. I can add more about this if you like
Or you could just use a UK SIM. 3 options worth looking at are: O2's My Europe Extra, with £10 a month fee then free incoming calls, outgoing 25p/min; Vodafone Passport, with 75p connect fee, then no further charge for incoming, same rates as at home for outgoing; or 3, with the cheapest ordinary roaming at 10p/min incoming, 25p/min outgoing