Would you suspect old switch's for intermittent network problems?

regarding cabling problems.... wouldn't something like that have been an issue from the start?  And wouldn't they not be intermittent?  

We have run fine for many months.   Then suddenly itermittant problems.  By that I mean, we run 100% fine for hours a day, then suddenly all 48 stations will start having problems.

With that in mind, does this still sound like cabling could be an issue?

Just to be clear -- it does not seem like interference between the voip box and the telephone -- it seems to be some sort of network issue.  When it gets bad enough it throws the VIOP boxes out of sync.  

There is a voip box and the remote office, and then one at the HQ.  It basically converts to VOIP and then back again.  When the box's get out of sync, lots or all of the lines will get fast busy at the remote office, and the box's have to be reset.  

I would suspect the VOIP box's but there are multiple sets and it doesnt make sense for them to all go bad at once.

A question about this cabling thing.  Could interference in 1 or a few cables, cause problems with more than just those cables?  (i.e. could it do something weird to the switch so that traffic on other cables also became affected due to the switch being affected?)