The "magic cure" for many wireless connection problems is to reboot the router. Give that a try, if you haven't already. (it helps if the problem is caused by "IP conflicts" - where the router is trying to allocate the same IP address to more than one device). It's usually best to do it late morning - that will help avoid the risk of losing speed on your broadband connections. Also, don't try rebooting too many times one after the other or your exchange may "see" it as a problem with the line and slow you down to "cure" it.
Failing that, it may help to change the broadcast channel on your router. Wifi is broadcast on 11 or 13 channels (depending where in the world you live) and if there are other routers using the same channel as you within range, they may swamp your signal out and your phone may be trying to connect to those signals instead. A simple, free way to check that is to download and run a PC tool called inSSider - that will show you what channels are being used near you and how strong the signal from them is in your house. You can then set your router to use a channel that is least used or weakest used by other signals.
