We all know this is a pretty busy market but if you’ve got a good idea for an app then it is definitely worth pursuing. HeyWire know all about this strategy and have produced a top notch Facebook app that allows users to send both texts and tweets within Facebook itself. , There is a charge though, not per message, but to give you a phone number to use; HeyWire will charge 20 Facebook credits per month. This telephone number allows you to send a receive free SMS messages from USA, Canada, Caribbean, Mexico, South & Central America and China. This is a little annoying, although it’s not likely to…