When I visit London this fall I will bring an unlocked GSM cell phone. I will purchase a SIM card to use with the phone so I am asking for any advance/tips from recent London visitors so I won't stumble in the process of getting the phone operational. I would like to know the retailer from whom you purchased the card, the name of the wireless service, and any pro's and con's related to the transaction. The card will have a 30 day roll over (ie, pay go), and the phone will be mainly used as an electronic guide for my travel in and around London; phone calls will be kept to a minimum (I will be using MagicJack to phone to the USA).
About ten years ago when I first visited London I went to a Car Phone Warehouse where the staff set me up with an inexpensive flip phone. They did all the work to get the phone operational and I left as a satisfied customer. In 2014 I decided to get a phone from Argos that was located in a Sainsbury's. The sales person knew very little about getting a phone operational; all that person did was give me a box with a phone in it and a SIM card and send me on my way. I wasn't happy about the treatment. This time I want to walk from the retail establishment with an operational phone in hand.