Nokia C5-03 and the blind user.....

Question

I bought my C5-03 last year because it had good voice controlled dialing and walking sat nav - which was brilliant when it worked.  I now have two major problems that are reducing the usefulness of the phone as a basic voice call device and as a navigation guide.
The walking sat nav is now very edgy as the signal strength in the Reading, UK area appears to have dropped away and I seldom see 3 bars on the GPS 'status' graph.  I'm assuming that's poor Thames Valley coverage rather than a duff handset.
The other, more acute, issue is that I need to be able to answer the phone by one keypress.  Yes, that has been set-up - but my handset routes the sound output from the caller to the wired headset and not to the handset 'speaker'  by default.  There does not appear to be a way that I can set the inbuilt earphone to route the caller's voice  to the handset - rather than the headset!  Surely, there's a menu in there somewhere that will mean that when I get a call, I don't have to both acknowledge the call <and> select the in-built earphone. option (I think that comes-up at the bottom right of the screen area (a toggle between handset and headset?).
How can I configure the phone to hear the caller's voice through the in-built earphone, by default - when the headset is not plugged-in?  It seems crazy that when the headset is not present, that the system does not automatically route the incoming caller's voice to the handset earphone.   
Before we go round the update route, I have already got the latest phone software download (12.0. 023).  I did a 'hard reset' yesterday, too.
Please help!

Answer 1

Something I did over the last day has resolved the call answering issue. Might be an intermittent hardware fault, I suppose. No doubt it will reoccur when I most need the phone! Re the sat signal; that seems really variable. Watch this space - but don't hold your collective breath!