This indeed is a shortcoming of all HTC phones and their assumptions of market requirements, akin to their biggest boo-boo to date:
To only allow US zip code entries in the People app when creating addresses manually. Not useful at all when HTC released the phone in the UK market first. Doh!
This is now fixed of course, but it shows the lack of joined up planning when they designed the software. This is another such boo-boo IMO.
It is assumed that the wifi adapter will connect to the strongest signal to give us all the best connection experience possible, however with the proliferation of open wifi signals now on offer in the UK (Openzone and BTFON etc) it is now causing havoc when we all don't have BT as an ISP.
Currently the priority of the Sensation's wifi radio software is to connect to an open signal first. Second, the strongest.
Unlike an alternative Apple product, the HTC does not have any settings to set a preference for remembered wireless networks and to only apply the other default rules AFTER those preferences. The Apple product also never connects to a network without the okay from the user. The HTC software connects irrespective. Finally the "forget network" option doesn't work either, as it rescans, picks it up again straight away and if open, tries to connect again.
This always happens in my home as the BTFON signal from next door's BT router is actually stronger at the front of my house that my own router signal from the back. Before anyone says "get another router or position it somewhere else", I can't without spending at least £60+ for a SKY ANYTIME+ wireless receiver (which I refuse to do).
I have SKY+ HD (currently being pushed heavily at only an extra £10 pm) and in order to get the Anytime+ service, it downloads via LAN cable directly from the sky router into the back of the Sky box. I don't want LAN cables around my house, so I moved the router next to the sky box. Trouble is there are so many magnetic signals in that corner of the room (with my TV, surround sound etc) AND the sky router is a locked SAGEM and totally crap wifi -wise (another known issue) that signal strength across my house is weak. It is a modern house (<10years old) with thin stud walls too.
The solution is for HTC to:
1) re-configure their wifi app to manage discovered networks better.
2) allow us to control which networks we wish our phone to connect automatically too.
3) allow an option to set a flag to ignore other found wifi networks, regardless of signal strength.
4) allow a selectable period frequency for auto rescans.
However all these fly in the face of the original idea of the Sensation and HTC, which was to produce a phone that connects to any network as silently and quickly as possible. HTC's "Watch" app and service launched specifically with the Sensation wouldn't have been so great without it.
The only solution left until this happens is to boost your wireless router signal as best as you can.
In the meatime, I have posted these to HTC as bugs. Any reply and I will update.