I have an iPhone and an iPad, and I think that you will not have a problem hearing when you use the iPhone. It has a volume control, it can also be placed on speaker, and if you wanted to, you could even use it with headphones, with the headphone jack.
I love taking pictures with the iPhone because it puts the pictures right into my Photostream, and I then have the picture right on the Ipad and the MacAir, without having to download or do anything.
Then, I use the iPad (which is easier for me to see what i am doing) and do any necessary photo editing.
With the iPhone, you can get iMessages, just like you do on the iPad, and you can also get regular text messages like you would on any other cell phone.
I don't do any surfing on my iPhone because I have the iPad, but I can do that as well when necessary.
Another thing that i like is when I want to listen to music or a motivational tape when i go to bed, I use the headphones, and it is a whole lot easier than packing the iPad to bed with me.
All in all, I think the iPhone is a great phone, and I would not want to go back to any other phone after having mine for the last year.